Wireless power transfer system coil arrangements and method of operation

ABSTRACT

This disclosure provides systems, methods and apparatus for wireless power transfer and particularly wireless power transfer to remote systems such as electric vehicles. In one aspect the disclosure provides for an apparatus for wirelessly transmitting power. The apparatus includes a first conductive structure configured to generate a first magnetic field in response to receiving a first time-varying signal from a power source. The apparatus includes a second conductive structure configured to generate a second magnetic field in response to receiving a second time-varying signal from the power source. The first and second structures are positioned to maintain a substantial absence of mutual coupling between the first and second magnetic fields.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit under 35 U.S.C.§119(e) of U.S. Provisional Patent Application No. 61/699,717 entitled“WIRELESS POWER TRASFER SYSTEM COIL ARRANGEMENTS AND METHOD OFOPERATION” filed on Sep. 11, 2012, the disclosure of which is herebyincorporated by reference in its entirety. This application furtherclaims priority to and the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application No. 61/699,700 entitled “DEVICE, SYSTEMAND METHOD FOR CONTROL OF WIRELESS POWER TRANSFER” filed on Sep. 11,2012, the disclosure of which is hereby incorporated by reference in itsentirety. This application further claims priority to and the benefitunder 35 U.S.C. §119(e) of U.S. Provisional Patent Application No.61/704,265 entitled “COIL ARRANGEMENTS IN WIRELESS POWER TRANSFERSYSTEMS” filed on Sep. 21, 2012, the disclosure of which is herebyincorporated by reference in its entirety.

FIELD

The present disclosure relates generally to wireless power transfer, andmore specifically to devices, systems, and methods related to wirelesspower transfer to remote systems such as vehicles including batteries.More particularly, the present disclosure relates to coil arrangementsfor induction coils in a wireless power transfer system.

BACKGROUND

Remote systems, such as vehicles, have been introduced that includelocomotion power derived from electricity received from an energystorage device such as a battery. For example, hybrid electric vehiclesinclude on-board chargers that use power from vehicle braking andtraditional motors to charge the vehicles. Vehicles that are solelyelectric generally receive the electricity for charging the batteriesfrom other sources. Battery electric vehicles (electric vehicles) areoften proposed to be charged through some type of wired alternatingcurrent (AC) such as household or commercial AC supply sources. Thewired charging connections require cables or other similar connectorsthat are physically connected to a power supply. Cables and similarconnectors may sometimes be inconvenient or cumbersome and have otherdrawbacks. Wireless charging systems that are capable of transferringpower in free space (e.g., via a wireless field) to be used to chargeelectric vehicles may overcome some of the deficiencies of wiredcharging solutions. As such, wireless charging systems and methods thatefficiently and safely transfer power for charging electric vehicles aredesirable.

SUMMARY

Various implementations of systems, methods and devices within the scopeof the appended claims each have several aspects, no single one of whichis solely responsible for the desirable attributes described herein.Without limiting the scope of the appended claims, some prominentfeatures are described herein.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

One aspect of the disclosure provides an apparatus for wirelesslytransmitting power. The apparatus includes a first conductive structureconfigured to generate a first magnetic field in response to receiving afirst time-varying signal from a power source. The apparatus furtherincludes a second conductive structure configured to generate a secondmagnetic field in response to receiving a second time-varying signalfrom the power source. The first and second structures are positioned tomaintain a substantial absence of mutual coupling between the first andsecond magnetic fields.

Another aspect of the disclosure provides an implementation of a methodof wirelessly transmitting power. The method includes generating a firstmagnetic field via a first conductive structure in response to receivinga first time-varying signal from a power source. The method furtherincludes generating a second magnetic field via a second conductivestructure in response to receiving a second time-varying signal from thepower source. The first and second structures are positioned to maintaina substantial absence of mutual coupling between the first and secondmagnetic fields.

Yet another aspect of the disclosure provides an apparatus forwirelessly transmitting power. The apparatus includes a first means forgenerating a first magnetic field in response to receiving a firsttime-varying signal from a power source. The apparatus further includesa second means for generating a second magnetic field in response toreceiving a second time-varying signal from the power source. The firstand second generating means are positioned to maintain a substantialabsence of mutual coupling between the first and second magnetic fields.

Another aspect of the subject matter described in the disclosureprovides an apparatus for wirelessly transmitting power. The apparatusincludes a first conductive structure configured to generate a firstmagnetic field based on a first current received from a power source.The apparatus further includes a second conductive structure configuredto generate a second magnetic field based on a second current from thepower source. The apparatus further includes a controller configured todetermine a respective coupling coefficient between each of the firstand second conductive structures and a third conductive structureconfigured to receive power via the first or the second magnetic field.The controller is further configured to adjust the first or secondcurrent applied to the first and second conductive structures based atleast in part on the coupling coefficients.

Another aspect of the subject matter described in the disclosureprovides an implementation of a method for wirelessly transmittingpower. The method includes generating a first magnetic field via a firstconductive structure based on a first current received from a powersource. The method further includes generating a second magnetic fieldvia a second conductive structure based on a second current from thepower source. The method further includes determining a respectivecoupling coefficient between each of the first and second conductivestructures and a third conductive structure configured to receive powervia the first or the second magnetic field. The method further includesadjusting the first or second current applied to the first and secondconductive structures based at least in part on the couplingcoefficients.

Another aspect of the subject matter described in the disclosureprovides an apparatus for wirelessly transmitting power. The apparatusincludes a first means for generating a first magnetic field via basedon a first current received from a power source. The apparatus furtherincludes a second means for generating a second magnetic field based ona second current from the power source. The apparatus further includesmeans for determining a respective coupling coefficient between each ofthe first and second generating means and a means for receiving powervia the first or the second magnetic field. The apparatus furtherincludes means for adjusting the first or second current applied to thefirst and second generating means based at least in part on the couplingcoefficients.

Another aspect of the subject matter described in the disclosureprovides an apparatus for wirelessly receiving power. The apparatusincludes a first conductive structure configured to wirelessly receivepower via a magnetic field generated by a transmitter conductivestructure having a length greater than a width. The first conductivestructure has a length greater than a width. The first conductivestructure includes a first loop and a second loop enclosing a first areaand a second area, respectively. The first loop has a first lowersurface and the second loop has a second lower surface that aresubstantially coplanar. The first conductive structure has a first edgeand a second edge each intersecting a first geometric line running alongthe length of the first conductive structure. The apparatus furtherincludes a second conductive structure configured to wirelessly receivepower via the magnetic field. The second conductive structure encloses athird area and having a length greater than a width. The first geometricline runs along the length of the second conductive structure. The firstgeometric line is substantially perpendicular to a second geometric linerunning along the length of the transmitter conductive structure.

Another aspect of the disclosure provides an implementation of a methodof wirelessly receiving power. The method includes wirelessly receivingpower, at a first conductive structure, via a magnetic field generatedby a transmitter conductive structure having a length greater than awidth. The first conductive structure has a length greater than a width.The first conductive structure includes a first loop and a second loopenclosing a first area and a second area, respectively. The first loophas a first lower surface and the second loop has a second lower surfacethat are substantially coplanar. The first conductive structure has afirst edge and a second edge each intersecting a first geometric linerunning along the length of the first conductive structure. The methodfurther includes wirelessly receiving power, at a second conductivestructure, via the magnetic field. The second conductive structureencloses a third area and has a length greater than a width. The firstgeometric line runs along the length of the second conductive structure.The first geometric line is substantially perpendicular to a secondgeometric line running along the length of the transmitter conductivestructure.

Another aspect of the disclosure provides an apparatus for wirelesslyreceiving power. The apparatus includes a first means for wirelesslyreceiving power via a magnetic field generated by a transmitterconductive structure having a length greater than a width. The firstreceiving means has a length greater than a width. The first receivingmeans includes a first loop and a second loop enclosing a first area anda second area, respectively. The first loop has a first lower surfaceand the second loop has a second lower surface that are substantiallycoplanar. The first receiving means has a first edge and a second edgeeach intersecting a first geometric line running along the length of thefirst receiving means. The apparatus further includes a second means forwirelessly receiving power via the magnetic field, the second receivingmeans enclosing a third area and having a length greater than a width.The first geometric line runs along the length of the second receivingmeans. The first geometric line is substantially perpendicular to asecond geometric line running along the length of the transmitterconductive structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary wireless power transfer system forcharging an electric vehicle, in accordance with an exemplaryembodiment.

FIG. 2 is a schematic diagram of exemplary components of the wirelesspower transfer system of FIG. 1.

FIG. 3 is a perspective view illustration of exemplary induction coilsused in an electric vehicle wireless power transfer system.

FIG. 4 is a diagram illustrative of the spatial distribution of powercontributions of the coils shown in FIG. 3 during wireless powertransfer.

FIG. 5 is a perspective view illustration of induction coils of awireless power transmitter apparatus according to an exemplaryembodiment.

FIG. 6 is a perspective view illustration of induction coils of awireless power transmitter apparatus according to another exemplaryembodiment.

FIG. 7 is a perspective view illustration of induction coils in awireless power transfer system according to an exemplary embodiment.

FIG. 8 is a diagram illustrative of the spatial distribution of powercontributions of the coils shown in FIG. 7 during wireless powertransfer.

FIG. 9 is a perspective view illustration of induction coils in awireless power transfer system according to an exemplary embodiment.

FIG. 10 is a diagram illustrative of the spatial distribution of powercontributions of the coils shown in FIG. 9 during wireless powertransfer.

FIG. 11 is a perspective view illustration of induction coils in awireless power transfer system according to an exemplary embodiment.

FIG. 12 is a diagram illustrative of the spatial distribution of powercontributions of the coils shown in FIG. 11 during wireless powertransfer.

FIG. 13 is a perspective view illustration of induction coils in awireless power transfer system according to an exemplary embodiment.

FIG. 14 is a diagram illustrative of the spatial distribution of powercontributions of the coils shown in FIG. 13 during wireless powertransfer.

FIG. 15 is a perspective view illustration of induction coils in awireless power transfer system according to a further exemplaryembodiment.

FIG. 16 is a diagram illustrative of the spatial distribution of powercontributions of the coils shown in FIG. 15 during wireless powertransfer.

FIG. 17 is a perspective view illustration of induction coils in awireless power transfer system according to a still further exemplaryembodiment.

FIG. 18 is a diagram illustrative of the spatial distribution of powercontributions of the coils shown in FIG. 17 during wireless powertransfer.

FIG. 19 is a schematic diagram of induction coils in a wireless powertransfer system, in accordance with an exemplary embodiment.

FIG. 20 is a plot illustrating impedance of the induction coils as shownin FIG. 19 during wireless power transfer.

FIGS. 21A, 21B, and 21C are vector diagrams illustrating voltage andcurrent seen at the secondary inductive coil as shown in FIG. 19 duringwireless power transfer.

FIG. 22 is a functional block diagram showing exemplary core andancillary components of the wireless power transfer system of FIG. 1.

FIG. 23 is a flow chart of an exemplary method of operating a wirelesspower transfer system, in accordance with an exemplary embodiment.

FIG. 24 is a flow chart of another exemplary method of operating awireless power transfer system, in accordance with an embodiment.

FIG. 25 is a functional block diagram of a wireless power transmitter,in accordance with an embodiment.

FIG. 26 is a flow chart of another exemplary method of wirelesslyreceiving power, in accordance with an embodiment.

FIG. 27 is a functional block diagram of a wireless power receiver, inaccordance with an embodiment.

FIG. 28 is a flow chart of another exemplary method of operating awireless power transfer system, in accordance with an embodiment.

FIG. 29 is a functional block diagram of a wireless power transmitter,in accordance with an embodiment.

The various features illustrated in the drawings may not be drawn toscale. Accordingly, the dimensions of the various features may bearbitrarily expanded or reduced for clarity. In addition, some of thedrawings may not depict all of the components of a given system, methodor device. Finally, like reference numerals may be used to denote likefeatures throughout the specification and figures.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of theinvention and is not intended to represent the only embodiments in whichthe invention may be practiced. The term “exemplary” used throughoutthis description means “serving as an example, instance, orillustration,” and should not necessarily be construed as preferred oradvantageous over other exemplary embodiments. The detailed descriptionincludes specific details for the purpose of providing a thoroughunderstanding of the exemplary embodiments of the invention. It will beapparent to those skilled in the art that the exemplary embodiments ofthe invention may be practiced without these specific details. In someinstances, well-known structures and devices are shown in block diagramform in order to avoid obscuring the novelty of the exemplaryembodiments presented herein.

Wirelessly transferring power may refer to transferring any form ofenergy associated with electric fields, magnetic fields, electromagneticfields, or otherwise from a transmitter to a receiver without the use ofphysical electrical conductors (e.g., power may be transferred throughfree space). The power output into a wireless field (e.g., a magneticfield) may be received, captured by, or coupled by a “receiving coil” toachieve power transfer. It will be understood that, throughout thisspecification, two components being “coupled” may refer to theirinteraction through direct or indirect ways, and may further refer to aphysically connected (e.g., wired) coupling or a physically disconnected(e.g., wireless) coupling.

An electric vehicle is used herein to describe a remote system, anexample of which is a vehicle that includes, as part of its locomotioncapabilities, electrical power derived from a chargeable energy storagedevice (e.g., one or more rechargeable electrochemical cells or othertype of battery). As non-limiting examples, some electric vehicles maybe hybrid electric vehicles that include besides electric motors, atraditional combustion engine for direct locomotion or to charge thevehicle's battery. Other electric vehicles may draw all locomotionability from electrical power. An electric vehicle is not limited to anautomobile and may include motorcycles, carts, scooters, and the like.By way of example and not limitation, a remote system is describedherein in the form of an electric vehicle (EV). Furthermore, otherremote systems that may be at least partially powered using a chargeableenergy storage device are also contemplated (e.g., electronic devicessuch as personal computing devices and the like).

Inductive power transfer (IPT) systems are one way for the wirelesstransfer of energy. In IPT, a primary (or “transmitter”) power devicetransmits power to a secondary (or “receiver”) power receiver device.Each of the transmitter and receiver power devices include inductors,typically an arrangement of coils or windings of electric currentconveying media. An alternating current in the primary inductor producesa fluctuating electromagnetic field. When the secondary inductor isplaced in proximity to the primary inductor, the fluctuatingelectromagnetic field induces an electromotive force (EMF) in thesecondary inductor, thereby transferring power to the secondary powerreceiver device.

In electric vehicle and plug-in hybrid vehicle IPT systems the primarypower device may be situated on the ground and may be referred to as a“base” device or power pad. The secondary power device may be situatedon the electric vehicle and may be referred to as a “pick-up” device orpower pad. These devices are commonly used to transmit power from thebase (transmitter) device to the pick-up (receiver) device. Some IPTsystems are also able to function in a mode in which power istransferred the other way, i.e. from the pick-up device to the basedevice. In this mode, the pick-up device functions as the “primary”device and the base device functions as the “secondary” device becausethe pick-up induces an EMF in the base. This may allow power stored inan electric vehicle battery to be transferred back to a mainselectricity grid.

PCT publication No. WO 2010/090539 discloses an IPT system for poweringelectric vehicles in which a base (usually the primary) coils includetwo separate co-planar coils positioned above a core formed from amaterial of high magnetic permeability, such as ferrite. In thisarrangement, there is no straight path through the core that passesthrough the coils. The coils act as pole areas and lines of magneticflux arc between them in the form of a “flux pipe” above the coils, azone of high flux concentration. The arrangement is considered to resultin little leakage of flux below the coils on the side of the core.

The same publication also discloses the use of three coils in the coilarrangement of the receiver (pick-up) device. The first two coils areseparate co-planar coils as in the base coil arrangement. Duringcharging, these two coils are aligned with the co-planar coils in thebase device. The third coil is positioned centrally above the other twocoils on the same side of the magnetically permeable core. The thirdcoil allows power to be extracted from the vertical component of themagnetic field intercepted by the receiver device in addition to thehorizontal component, which is extracted by the first two, co-planarcoils. The co-planar coils are considered to have good tolerance tomisalignment between the transmitter and receiver devices in thedirection perpendicular to a line between the centers of the co-planarcoils but less tolerance to misalignment in the direction parallel tothe line between the centers of the co-planar coils. The three coilarrangement in the receiver device is considered to improve thetolerance of the IPT system in the parallel direction, thus increasingthe overall tolerance of the system to misalignment in any direction.

PCT publication No. WO 2011/016737 describes an IPT system for poweringelectric vehicles in which a base coil arrangement includes twooverlapping planar coils that are magnetically decoupled. Some coilarrangements increase complexity and cost and may include non-trivialmutual coupling between the induction coils In one aspect, it may bedifficult to tailor to different types of IPT systems.

Thus, there remains a need for improved tolerance to IPT system coilmisalignment, both in the longitudinal (i.e. forwards/backwards relativeto the vehicle) direction and the transverse (i.e. side-to-side)direction.

In accordance with embodiments described herein, the IPT system may useresonant inductive coupling, in which power is transmitted betweeninductive coils that are tuned to resonate at substantially the samefrequency. Resonant coupling may be achieved by adding inductive and/orcapacitive elements in series or parallel with the induction coils orvia selecting coils with a selected inherent capacitance (e.g.,self-resonant).

In a resonant IPT system, the proportion of available power transferredto the pick-up is dependent on the degree of coupling between theprimary and secondary coils. The greater the coupling, the more power istransferred to the secondary coil. The coupling coefficient may bedefined as the fraction of flux of the primary coil that cuts thesecondary coil, and is at least in part a function of the geometry ofthe system. The coupling coefficient is therefore at least in partdependent on the distance between the primary and secondary coils, andtheir alignment.

In wireless power transfer systems for charging electric vehicles usingIPT, there can be large variations in the level of coupling each time avehicle is charged. The distance and alignment between the primary andsecondary coils may vary based on the location of the coils and thepositioning of the vehicle, on which the pick-up is mounted, withrespect to the base. This can create difficulties with regard to thedemand on power electronic components in the system to compensate forthis variation, resulting in the need for more expensive components,reducing reliability and limiting operating range.

FIG. 1 is a diagram of an exemplary wireless power transfer system 100for charging an electric vehicle 112, in accordance with an exemplaryembodiment. The wireless power transfer system 100 enables charging ofan electric vehicle 112 while the electric vehicle 112 is parked near abase wireless charging system 102 a. Spaces for two electric vehiclesare illustrated in a parking area to be parked over corresponding basewireless charging system 102 a and 102 b. In some embodiments, a localdistribution center 130 may be connected to a power backbone 132 andconfigured to provide an alternating current (AC) or a direct current(DC) supply through a power link 110 to the base wireless chargingsystem 102 a. The base wireless charging system 102 a also includes abase system induction coil 104 a for wirelessly transferring orreceiving power. An electric vehicle 112 may include a battery unit 118,an electric vehicle induction coil 116, and an electric vehicle wirelesscharging system 114. The electric vehicle induction coil 116 mayinteract with the base system induction coil 104 a for example, via aregion of the electromagnetic field generated by the base systeminduction coil 104 a.

In some exemplary embodiments, the electric vehicle induction coil 116may receive power when the electric vehicle induction coil 116 islocated in an energy field produced by the base system induction coil104 a. The field corresponds to a region where energy output by the basesystem induction coil 104 a may be captured by an electric vehicleinduction coil 116. In some cases, the field may correspond to the “nearfield” of the base system induction coil 104 a. The near-field maycorrespond to a region in which there are strong reactive fieldsresulting from the currents and charges in the base system inductioncoil 104 a that do not radiate power away from the base system inductioncoil 104 a. In some cases the near-field may correspond to a region thatis within about ½π of wavelength of the base system induction coil 104 a(and vice versa for the electric vehicle induction coil 116) as will befurther described below.

Local distribution 130 may be configured to communicate with externalsources (e.g., a power grid) via a communication backhaul 134, and withthe base wireless charging system 102 a via a communication link 108.

In some embodiments the electric vehicle induction coil 116 may bealigned with the base system induction coil 104 a and, therefore,disposed within a near-field region simply by the driver positioning theelectric vehicle 112 correctly relative to the base system inductioncoil 104 a. In other embodiments, the driver may be given visualfeedback, auditory feedback, or combinations thereof to determine whenthe electric vehicle 112 is properly placed for wireless power transfer.In some embodiments, feedback may be generated by the wireless powertransfer system 100, for example, electric vehicle 112 or a processorconnected to a user interface of electric vehicle 112, or from a signalor sensor information that may be contained in the base wirelesscharging system 102 a. In yet other embodiments, the electric vehicle112 may be positioned by an autopilot system, which may move theelectric vehicle 112 back and forth (e.g., in zig-zag movements) untilan alignment error has reached a tolerable value. This may be performedautomatically and autonomously by the electric vehicle 112 without orwith only minimal driver intervention provided that the electric vehicle112 is equipped with a servo steering wheel, ultrasonic sensors, andintelligence to adjust the vehicle. In still other embodiments, theelectric vehicle induction coil 116, the base system induction coil 104a, or a combination thereof may have functionality for displacing andmoving the induction coils 116 and 104 a relative to each other to moreaccurately orient them and develop more efficient coupling therebetween.

The base wireless charging system 102 a may be located in a variety oflocations. As non-limiting examples, some suitable locations include aparking area at a home of the electric vehicle 112 owner, parking areasreserved for electric vehicle wireless charging modeled afterconventional petroleum-based filling stations, and parking lots at otherlocations such as shopping centers and places of employment.

Charging electric vehicles wirelessly may provide numerous benefits. Forexample, charging may be performed automatically, virtually withoutdriver intervention and manipulations thereby improving convenience to auser. There may also be no exposed electrical contacts and no mechanicalwear out, thereby improving reliability of the wireless power transfersystem 100. Manipulations with cables and connectors may not be needed,and there may be no cables, plugs, or sockets that may be exposed tomoisture and water in an outdoor environment, thereby improving safety.There may also be no sockets, cables, and plugs visible or accessible,thereby reducing potential vandalism of power charging devices. Further,since an electric vehicle 112 may be used as distributed storage devicesto stabilize a power grid, a docking-to-grid solution may be used toincrease availability of vehicles for Vehicle-to-Grid (V2G) operation.

A wireless power transfer system 100 as described with reference to FIG.1 may also provide aesthetical and non-impedimental advantages. Forexample, there may be no charge columns and cables that may beimpedimental for vehicles and/or pedestrians.

As a further explanation of the vehicle-to-grid capability, the wirelesspower transmit and receive capabilities may be configured to bereciprocal such that the base wireless charging system 102 a transferspower to the electric vehicle 112 and the electric vehicle 112 transferspower to the base wireless charging system 102 a e.g., in times ofenergy shortfall. This capability may be useful to stabilize the powerdistribution grid by allowing electric vehicles to contribute power tothe overall distribution system in times of energy shortfall caused byover demand or shortfall in renewable energy production (e.g., wind orsolar).

It will be therefore understood that the terms “transmitter,”“receiver,” “primary,” and “secondary” and the like are used herein torefer to the uses of the components of the wireless power transfersystem when used for transferring power from the power supply to theelectric vehicle, i.e. from the transmitter or primary device to thereceiver or secondary device. However, the wireless power transfersystem may involve the use of these components to transfer some power,which in some embodiments may only be a small amount, in the oppositedirection, for example to transfer energy from the electric vehicle tothe power distribution grid, as part of a process to improve alignmentof the transmitter and receiver devices, or to identify whichtransmitter device is appropriately placed for transferring power to thereceiver device. Therefore the “transmitter” may also be used to receivepower and the “receiver” may also be used to transmit power. The use ofthese terms, although referring to the normal sense of operation ofcertain components of the system for ease of understanding, does notlimit embodiments to any particular operation of such components.

FIG. 2 is a schematic diagram of exemplary components of the wirelesspower transfer system 100 of FIG. 1. As shown in FIG. 2, the wirelesspower transfer system 200 may include a base system transmit circuit 206including a base system induction coil 204 having an inductance L₁. Thewireless power transfer system 200 further includes an electric vehiclereceive circuit 222 including an electric vehicle induction coil 216having an inductance L₂. Embodiments described herein may usecapacitively loaded wire loops (i.e., multi-turn coils) forming aresonant structure that is capable of efficiently coupling energy from aprimary structure (transmitter) to a secondary structure (receiver) viaa magnetic or electromagnetic near field if both primary and secondaryare tuned to a common resonant frequency.

A resonant frequency may be based on the inductance and capacitance of atransmit circuit including an induction coil (e.g., the base systeminduction coil 204) as described above. As shown in FIG. 2, inductancemay generally be the inductance of the induction coil, whereas,capacitance may be added to the induction coil to create a resonantstructure at a desired resonant frequency. As a non-limiting example, acapacitor may be added or may be integrated with the induction coil, andarranged to be in series with the induction coil to create a resonantcircuit (e.g., the base system transmit circuit 206) that generates anelectromagnetic field. Accordingly, for larger diameter induction coils,the value of capacitance for inducing resonance may decrease as thediameter or inductance of the coil increases. Inductance may also dependon a number of turns of an induction coil. Furthermore, as the diameterof the induction coil increases, the efficient energy transfer area ofthe near field may increase. Other resonant circuits are possible. Asanother non limiting example, a capacitor may be placed in parallelbetween the two terminals of the induction coil (e.g., a parallelresonant circuit). Furthermore an induction coil may be designed to havea high quality (Q) factor to improve the resonance of the inductioncoil.

Coils adapted for use in resonant structures may be used for theelectric vehicle induction coil 216 and the base system induction coil204. Using resonant structures for coupling energy may be referred to“magnetic coupled resonance,” “electromagnetic coupled resonance,”and/or “resonant induction.” The operation of the wireless powertransfer system 200 will be described based on power transfer from abase wireless power charging system 202 to an electric vehicle 112, butis not limited thereto. For example, as discussed above, the electricvehicle 112 may transfer power to the base wireless charging system 102a.

With reference to FIG. 2, a power supply 208 (e.g., AC or DC) suppliespower P_(SDC) to the base wireless power charging system 202 to transferenergy to an electric vehicle 112. The base wireless power chargingsystem 202 includes a base charging system power converter 236. The basecharging system power converter 236 may include circuitry such as anAC/DC converter configured to convert power from standard mains AC to DCpower at a suitable voltage level, and a DC/low frequency (LF) converterconfigured to convert DC power to power at an operating frequencysuitable for wireless high power transfer. The base charging systempower converter 236 supplies power P₁ to the base system transmitcircuit 206 including a base charging system tuning circuit 205 whichmay consist of reactive tuning components in a series or parallelconfiguration or a combination of both with the base system inductioncoil 204 to emit an electromagnetic field at a desired frequency. Thecapacitor C₁ (not shown) may be provided to form a resonant circuit withthe base system induction coil 204 that resonates at a desiredfrequency. The base system induction coil 204 receives the power P₁ andwirelessly transmits power at a level sufficient to charge or power theelectric vehicle 112. For example, the power level provided wirelesslyby the base system induction coil 204 may be on the order of kilowatts(kW) (e.g., anywhere from 1 kW to 110 kW or higher or lower).

Both the base system transmit circuit 206, which includes the basesystem induction coil 204, and the electric vehicle receive circuit 222,which includes the electric vehicle induction coil 216, may be tuned tosubstantially the same frequencies and may be positioned within thenear-field of an electromagnetic field transmitted by one of the basesystem induction coil 204 and the electric vehicle induction coil 116.In this case, the base system induction coil 204 and electric vehicleinduction coil 116 may become coupled to one another such that power maybe transferred to the electric vehicle receive circuit 222 including anelectric vehicle charging system tuning circuit 221 and electric vehicleinduction coil 216. The electric vehicle charging system tuning circuit221 may be provided to form a resonant circuit with the electric vehicleinduction coil 216 that resonates at a desired frequency. The mutualcoupling coefficient resulting at coil separation is represented byelement k(d). Equivalent resistances R_(eq,1) and R_(eq,2) represent thelosses that may be inherent to the induction coils 204 and 216 and anyanti-reactance capacitors that may, in some embodiments, be provided inthe base charging system tuning circuit 205 and electric vehiclecharging system tuning circuit 221 respectively. The electric vehiclereceive circuit 222 including the electric vehicle induction coil 216and electric vehicle charging system tuning circuit 221 receives powerP₂ and provides the power P₂ to an electric vehicle power converter 238of an electric vehicle charging system 214.

The electric vehicle power converter 238 may include, among otherthings, a LF/DC converter configured to convert power at an operatingfrequency back to DC power at a voltage level matched to the voltagelevel of an electric vehicle battery unit 218. The electric vehiclepower converter 238 may provide the converted power P_(LDC) to chargethe electric vehicle battery unit 218. The power supply 208, basecharging system power converter 236, and base system induction coil 204may be stationary and located at a variety of locations as discussedabove. The battery unit 218, electric vehicle power converter 238, andelectric vehicle induction coil 216 may be included in an electricvehicle charging system 214 that is part of electric vehicle 112 or partof the battery pack (not shown). The electric vehicle charging system214 may also be configured to provide power wirelessly through theelectric vehicle induction coil 216 to the base wireless power chargingsystem 202 to feed power back to the grid. Each of the electric vehicleinduction coil 216 and the base system induction coil 204 may act astransmit or receive induction coils based on the mode of operation.

While not shown, the wireless power transfer system 200 may include aload disconnect unit (LDU) to safely disconnect the electric vehiclebattery unit 218 or the power supply 208 from the wireless powertransfer system 200. For example, in case of an emergency or systemfailure, the LDU may be triggered to disconnect the load from thewireless power transfer system 200. The LDU may be provided in additionto a battery management system for managing charging to a battery, or itmay be part of the battery management system.

Further, the electric vehicle charging system 214 may include switchingcircuitry (not shown) for selectively connecting and disconnecting theelectric vehicle induction coil 216 to the electric vehicle powerconverter 238. Disconnecting the electric vehicle induction coil 216 maysuspend charging and also may adjust the “load” as “seen” by the basewireless charging system 102 a (acting as a transmitter), which may beused to decouple the electric vehicle charging system 114 (acting as thereceiver) from the base wireless charging system 102 a. The load changesmay be detected if the transmitter includes the load sensing circuit.Accordingly, the transmitter, such as a base wireless charging system202, may have a mechanism for determining when receivers, such as anelectric vehicle charging system 114, are present in the near-field ofthe base system induction coil 204.

As described above, in operation, assuming energy transfer towards thevehicle or battery, input power is provided from the power supply 208such that the base system induction coil 204 generates a field forproviding the energy transfer. The electric vehicle induction coil 216couples to the radiated field and generates output power for storage orconsumption by the electric vehicle 112. As described above, in someembodiments, the base system induction coil 204 and electric vehicleinduction coil 116 are configured according to a mutual resonantrelationship such that when the resonant frequency of the electricvehicle induction coil 116 and the resonant frequency of the base systeminduction coil 204 are very close or substantially the same, energy istransferred highly efficiently. Transmission losses between the basewireless power charging system 202 and electric vehicle charging system214 are minimal when the electric vehicle induction coil 216 is locatedin the near-field of the base system induction coil 204.

As stated, an efficient energy transfer occurs by coupling a largeportion of the energy in the near field of a transmitting induction coilto a receiving induction coil rather than propagating most of the energyin an electromagnetic wave to the far-field. When in the near field, acoupling mode may be established between the transmit induction coil andthe receive induction coil. The area around the induction coils wherethis near field coupling may occur is referred to herein as a near fieldcoupling mode region.

While not shown, the base charging system power converter 236 and theelectric vehicle power converter 238 may both include an oscillator, adriver circuit such as a power amplifier, a filter, and a matchingcircuit for efficient coupling with the wireless power induction coil.The oscillator may be configured to generate a desired frequency, whichmay be adjusted in response to an adjustment signal. The oscillatorsignal may be amplified by a power amplifier with an amplificationamount responsive to control signals. The filter and matching circuitmay be included to filter out harmonics or other unwanted frequenciesand match the impedance of the power conversion module to the wirelesspower induction coil. The power converters 236 and 238 may also includea rectifier and switching circuitry to generate a suitable power outputto charge the battery.

The electric vehicle induction coil 216 and base system induction coil204 as described throughout the disclosed embodiments may be referred toor configured as “loop” antennas, and more specifically, multi-turn loopantennas. The induction coils 204 and 216 may also be referred to hereinor be configured as “magnetic” antennas. The coil may also be referredto as an “antenna” of a type that is configured to wirelessly output orreceive power. As used herein, coils 204 and 216 are examples of “powertransfer components” of a type that are configured to wirelessly output,wirelessly receive, and/or wirelessly relay power. Loop (e.g.,multi-turn loop) antennas may be configured to include an air core or aphysical core such as a ferrite core. An air core loop antenna may allowthe placement of other components within the core area. Physical coreantennas including ferromagnetic or ferrimagnetic materials may allowdevelopment of a stronger electromagnetic field and improved coupling.

In this specification the term “coil” is used in the sense of alocalized winding arrangement having a number of turns of electricallyconducting material that all wind around one or more central points. Theterm “coil arrangement” is used to mean any winding arrangement ofconducting material, which may comprise a number of “coils.”

As discussed above, efficient transfer of energy between a transmitterand receiver occurs during matched or nearly matched resonance between atransmitter and a receiver. However, even when resonance between atransmitter and receiver are not matched, energy may be transferred at alower efficiency. Transfer of energy occurs by coupling energy from thenear field of the transmitting induction coil to the receiving inductioncoil residing within a region (e.g., within a predetermined frequencyrange of the resonant frequency, or within a predetermined distance ofthe near-field region) where this near field is established rather thanpropagating the energy from the transmitting induction coil into freespace.

As described above, according to some embodiments, coupling powerbetween two induction coils that are in the near field of one another isdisclosed. As described above, the near field may correspond to a regionaround the induction coil in which electromagnetic fields exist.Near-field coupling-mode regions may correspond to a volume that is nearthe physical volume of the induction coil, typically within a smallfraction of the wavelength. According to some embodiments,electromagnetic induction coils, such as single and multi-turn loopantennas, are used for both transmitting and receiving since magneticnear field amplitudes in practical embodiments tend to be higher formagnetic type coils in comparison to the electric near fields of anelectric type antenna (e.g., a small dipole). This allows forpotentially higher coupling between the pair. Furthermore, “electric”antennas (e.g., dipoles and monopoles) or a combination of magnetic andelectric antennas may be used.

FIG. 3 is a perspective view illustration of induction coils used in anelectric vehicle wireless power transfer system 300. The wireless powertransfer system comprises base or transmitter wireless power transferdevice which includes transmitter coil arrangement 301 and a pick-up orreceiver wireless power transfer device which includes receiver coilarrangement 302. Only the coils of the system 300 are shown in FIG. 3for clarity purposes. The system 300 may include one or more additionalcomponents as described, for example, with reference to FIGS. 1 and 2,and as otherwise described herein. The transmitter coils 301 may, forexample, form part of a wireless power transmitter apparatus situated onthe ground in a vehicle parking space while the receiver coils 302 may,for example, form part of a wireless power receiver device located onthe underside of an electric vehicle. For the purposes of thisspecification, it may be assumed that the coils in FIG. 3 and alldiagrams of a similar nature as described below are viewed in thelongitudinal direction of the electric vehicle. FIG. 3 shows receivercoils 302 positioned over transmitter coils 301, a position suitable forwireless power transfer between the transmitter and receiver coils 301and 302 upon energizing the transmitter coils 301.

In the configuration of FIG. 3, transmitter coils 301 comprise twosubstantially co-planar transmitter coils 303 a and 303 b connected toone or more power sources (not shown). In an embodiment, electriccurrent flows in the same direction in the adjacent portions of the twocoils 303 a and 303 b and the current in these adjacent portions hassubstantially the same magnitude and phase.

Receiver coils 302 comprise two substantially co-planar receiver coils304 a and 304 b and a third coil 305 positioned over the co-planarreceiver coils 304 a and 304 b. The coils in coil arrangement 302 may beconnected to a battery of the electric vehicle.

Both transmitter and receiver coil arrangements 301 and 302 areassociated with magnetically permeable members such as ferrite cores(not shown) positioned under the transmitter coils 301 and above thereceiver coils 302. To transfer power using the coils 301 and 302 ofFIG. 3, an alternating electric current is passed through thetransmitter coils 301. This creates a magnetic field in the form of a“flux pipe,” a zone of high flux concentration, looping above coilarrangement 301 between the holes in transmitter coils 303 a and 303 b.In use, receiver coils 302 are positioned such that the receiver coils304 and 305 intersect the lines of magnetic flux, thus inducing electriccurrent in the receiver coils 304 and 305, which is supplied to thebattery of the electric vehicle.

The co-planar receiver coils 304 a and 304 b extract power from thehorizontal components of magnetic flux generated by the transmittercoils 301. The single receiver coil 305 extracts power from the verticalcomponent of the magnetic flux generated by the transmitter coils. Thus,in combination, the coils of receiver coils 302 enable energy transferbetween the transmitter and receiver devices of the wireless powertransfer system. The operation and configuration as described withreference to FIG. 3 may analogously apply, where applicable, to thefurther embodiments described herein.

FIG. 4 is a diagram illustrative of the spatial distribution of powercontributions of the coils shown in FIG. 3 during wireless powertransfer. FIG. 4 depicts, in plan view, an area 400 covered by the coils300 of FIG. 3. The areas outlined in a broken line indicate approximateareas of power contribution from the transmitter coils 303 a and 303 bof transmitter coils 301 as shown in FIG. 3. The diagonally shaded areaindicates the approximate spatial distribution of power supplied to theco-planar receiver coils 304 a and 304 b while the dotted shaded areaindicates the approximate spatial distribution of power supplied to thesingle receiver coil 305. Thus, areas 401 and 402 represent theapproximate spatial distribution of power supplied to the singlereceiver coil 305 from the transmitter coils 303 a and 303 b, while area403 represents the approximate spatial distribution of power supplied tothe co-planar receiver coils 304 a and 304 b from the transmitter coils303 a and 303 b. It is noted that the spatial distribution of powercontributions may vary continuously across the area of the coils. Theareas shown in FIG. 4 and similar such diagrams elsewhere in thisspecification represent approximate areas of highest power contribution,for example the areas of power contribution above a certain threshold.

Line 404 shown in bold in FIG. 4 represents an estimated region oftolerance for the coil arrangements 300 shown in FIG. 3. That is, line404 marks the approximate area over which the centers of coilarrangements 301 and 302 may be misaligned before the amount of powertransfer between the coils falls below a certain level. It will beunderstood that line 404 is merely indicative of the tolerance regionresulting from the spatial power distributions of the coils of wirelesspower transfer system 300, it is exemplary and shown to illustraterelative spatial power distribution of the coils of the system 300.Likewise, the tolerance regions for further embodiments described hereinare exemplary and are shown to illustrate relative spatial distributionof the coils, for example, as compared to other embodiments describedherein.

The coil arrangement shown in FIG. 3 can be seen to have anapproximately circular tolerance region 404 in FIG. 4, meaning thedegree of misalignment between the transmitter and receiver coilarrangements that the system can withstand while still transferringpower reasonably efficiently is roughly equal in the longitudinal andtransverse directions.

As mentioned previously, it may be desirable for an electric vehicle IPTsystem to have flexibility in tolerance to suit the requirements of aparticular situation. For example, when an electric vehicle is manuallymaneuvered into position for charging, research has shown that humandrivers are better at judging vehicle alignment in the transversedirection than in the longitudinal direction. Therefore a human driveris more likely to position a vehicle correctly transversely thanlongitudinally. This might imply greater tolerance to misalignment inthe longitudinal direction would be desirable for a manually positionedvehicle.

On the other hand, in some situations, it may be beneficial to have agreater degree of tolerance to misalignment in the transverse direction.It is relatively easier to adjust the position of a vehiclelongitudinally simply by moving the vehicle backwards or forwards buttransverse re-alignment is more difficult and time consuming because itrequires a re-parking maneuver. This applies when a vehicle ispositioned for charging by an automatic control system or manually.

In addition, there may be regulatory issues with vehicles beingcontrolled entirely automatically, even when parking the vehicle over anIPT base device. Some systems allow the vehicle to control steering butrequire the driver to manually control the accelerator and brake. Insuch systems, greater alignment tolerance may be required in thelongitudinal direction, since the driver may be expected to be able toalign a vehicle less well than an automatic system in this direction.

Another consideration is that, due to regulations set by theInternational Commission on Non-Ionizing Radiation Protection (ICNIRP),it may be desirable to reduce the magnetic field emissions from thetransmitter device that may leak out beyond the boundaries of thevehicle, for example from the side of the vehicle, into areas wherepeople may be exposed to those emissions. These emissions may beparticularly present when a receiver device is misaligned. There may bean exponential increase of field emissions the closer the transmitterdevice is aligned to the side of the vehicle. In order to minimizeemissions, it is therefore desirable to optimize the transversealignment of the transmitter and receiver devices on an electricvehicle.

As such, the approximate tolerance region 404 for the coil arrangementshown in FIG. 3 may not be suitable for the alignment tolerancerequirements of electric vehicles in some situations.

In addition, the coil arrangement 302 on the electric vehicle side ofthe wireless power transfer system comprises three individual coils ofelectrically conducting material. This number of coils adds may add costto the manufacture of the electric vehicle on which the coil arrangement302 is mounted in some situations. The electronics required to operateand control this coil arrangement is also complex, adding further costto the manufacture of the electric vehicle. The size and complexity ofcoil arrangement 302 may also add weight to the electric vehicle,increasing running costs in certain scenarios.

FIG. 5 is a perspective view illustration of induction coils 500 of awireless power transmitter apparatus according to an embodiment. In use,the wireless power transfer transmitter device including transmittercoils 500 may be positioned on a ground surface, for example in a carpark, garage, charging station or the like.

Transmitter coils 500 comprises a first coil structure 501 and a secondcoil structure 502. The second coil structure 502 is positionedsubstantially centrally adjacent to the first coil structure 501, forexample under the first coil structure 501. In another embodiment, thesecond coil arrangement may be positioned over the first coil structure.

In the embodiment shown in FIG. 5, first coil structure 501 comprisestwo substantially co-planar transmitter coils 501 a and 501 b positionedadjacent to one another. Stated another way the first coil structure 501comprises first and second loops enclosing first and second areas,respectively. The first and second loops have lower surfaces that aresubstantially coplanar. In some embodiments the first coil structure 501is formed from a single coil (e.g., that may have one or more turns)that is wound to enclose the first and second areas. In otherembodiments, two separate coils 501 a and 501 b may be used. In use, theco-planar transmitter coils 501 a and 501 b may be able to be connectedto one or more electric power sources such that current flows clockwisearound one coil and counterclockwise around the other coil, i.e. suchthat electric current flows in the same direction in the adjacentportions of the two coils 501 a and 501 b. The co-planar transmittercoils 501 a and 501 b may be connected in series or parallel to the samepower source or alternatively they may be connected to a common powersource such that the current in the adjacent portions of the coils hassubstantially the same magnitude and phase.

The second coil structure 502 comprises a single planar transmitter coil502 in the embodiment shown in FIG. 5. Planar transmitter coil 502 ispositioned centrally under first coil arrangement 501 such that the holein planar transmitter coil 502 is aligned with a point between the twocoils 501 a and 501 b. Stated another way, the second transmitter coil502 encloses a third area and according to some embodiments may bepositioned such that substantially a center of the third area ispositioned substantially over a point between the two coils 501 a and501 b.

Furthermore, the end portions of transmitter coil 502 may generally beadjacent to spaces in respective interiors of co-planar transmittercoils 501 a and 501 b.

The overall transmitter coil arrangement 500 has a length along itslongitudinal axis, which is aligned with a line between the centers ofthe two coils 501 a and 501 b, that is greater than its width along atransverse axis, which is perpendicular to the longitudinal axis. Statedanother way, the first and second coil structures 501 and 502 havelengths longer than their widths. A geometric line running along thewidth of the first coil structure and between coils 501 a and 501 b isperpendicular to a geometric line running along the length.

In use, planar transmitter coil 502 is also connectable to an electricpower source.

The first and second coil structures 501 and 502 are configured suchthat, when powered, there is no mutual coupling between the magneticfields generated by each coil structure 501 and 502. For example, in theembodiment shown in FIG. 5, there is no mutual coupling between the coilstructures 501 and 502 as a result of the geometry of the configuration.The magnetic fields generated by the two coil structures add andsubtract from each other in different places over the area of the coilstructures 500, but the addition and subtraction is in equal parts suchthat there is no mutual coupling. In other words, the sum of themagnetic field produced by the first coil arrangement that intersectsthe second coil arrangement is substantially zero. In this way there isa substantial absence of mutual coupling between the coil structure 501and the coil structure 502. Stated another way, when a current (e.g., atime-varying signal) is applied to first coil structure 501,substantially zero voltage is generated in the second coil structure 502as a result of the current applied to the first coil structure 501.Likewise, when a current (e.g., a time-varying signal) is applied to thesecond coil structure 502, substantially zero voltage is generated inthe first coil structure 501 as a result of the current applied to thesecond coil structure 501. The first coil structure 501 may have asubstantially horizontally polarized magnetic moment and the second coilstructure 402 may have a substantially vertically polarized magneticmoment.

FIG. 6 is a perspective view illustration of induction coils 600 of awireless power transmitter apparatus according to another embodiment.Coil arrangement 600 is similar to coil arrangement 500 shown in FIG. 5and comprises a first coil structure 601 which itself comprisesco-planar transmitter coils 601 a and 601 b, and a second coil structure602 comprising a single planar transmitter coil 602. One differencebetween coil arrangement 600 and coil arrangement 500 is the size of theplanar transmitter coil 602. In the embodiment shown in FIG. 6,transmitter coil 602 covers an area similar to the area covered by thefirst coil structure 601. That is, the outermost lengths of conductingmaterial in each coil arrangement 601 and 602 are generally aligned.

A further embodiment comprises a first coil structure comprising asingle coil and a second coil structure also comprising a single coil.Again, the second coil arrangement is positioned centrally under thefirst coil arrangement such that there is no mutual coupling between themagnetic fields generated by the coils. This embodiment may be moredifficult to control and lead to smaller tolerance regions than, forexample, the embodiments shown in FIG. 5 and FIG. 6.

Coil arrangements 500 or 600 may be used in a wireless power transmitterapparatus in an electric vehicle wireless power transfer system. Whilenot shown in FIG. 5 or FIG. 6, wireless power transmitter apparatusesaccording to various embodiments (e.g., comprising one or morecomponents of FIG. 1 or 2 or otherwise described herein) may eachcomprise one or more magnetically permeable members magneticallyassociated with the coil arrangements 500 or 600. For example, ferritecores (not shown) may be positioned below the coil arrangements 500 or600. Magnetic shielding may also be used to contain the magnetic fieldsin the power transfer region and reduce energy losses. Such a system mayuse resonant inductive coupling between the transmitter and receiverdevices. Coil structures 501 and 502 may be tuned separately to eachother to achieve the resonant frequency. The tuning of the coilstructures 501 and 502 in the transmitter device may also take intoaccount the influence of coils of a receiver device and their tuning,particularly for closely coupled systems. For example, parallel-tunedreceiver coils may reduce the inductance of the transmitter coils so thetuning of the transmitter coils may be performed when the receiver coilsare present and short circuited.

Wireless power transmitter apparatuses according to various embodimentsas just described, for example with reference to FIGS. 5 and 6, providea number of benefits. Including both a co-planar coil structure 501 anda single coil 502 on the transmitter side of an electric vehicle IPTsystem allows for fewer components that may be required on the electricvehicle in a receiver structure as compared to some systems withoutadversely affecting power transfer rates or efficiency. This allows forreduced complexity and cost of electric vehicles. In addition, since thesingle coil 502 supplies flux in the vertical direction while theco-planar coils 501 supply flux in the horizontal direction, thetransmitter device can be tailored to produce magnetic flux field thatis tailored to the type or position of electric vehicle receiver deviceby changing the magnitude and phase of the current in the co-planar andsingle coils 501 and 502. Adjustment of the magnitude and phase of thecurrents in each coil may be done simultaneously. Having two coilarrangements providing power to the receiver coil also allows for therate and/or efficiency of wireless power transfer to be increased.Furthermore, the coils in the transmitter device can be configured toprovide different degrees of tolerance to misalignment, which may suitdifferent system requirements.

These and other benefits will now be discussed in relation to severalexemplary embodiments of electric vehicle IPT systems incorporatingwireless power transmitter apparatuses.

FIG. 7 is a perspective view illustration of induction coils 701 and 702in a wireless power transfer system 700 according to an exemplaryembodiment. The coils 701 and 702 illustrated in FIG. 7 may be used inan electric vehicle wireless power transfer system, for example. Thewireless power transfer system 700 comprises a wireless powertransmitter apparatus (of which only a portion of the coils is shown),which itself comprises a first coil structure 701 and a second coilstructure 704, and a wireless power transfer receiver device, whichitself comprises a receiver coil structure 702. Transmitter coilstructures 701 and 704 may be the same as coil structures 501 and 502 ofFIG. 5, respectively. Receiver coil structure 702 comprises a planarreceiver coil 705 that is configured to electrically connect to a load,for example wired connection to an electric vehicle battery. The coilsare shown in FIG. 7 in typical positions in an electric vehicle chargingsituation, with the receiver coil 705 positioned over the transmittercoil structures 701 and 704. In the position shown in FIG. 7, thewireless power transmitter and receiver coils 701 and 702 may beconsidered well aligned since the centers of the transmitter andreceiver coil arrangements 701 and 702 are in vertical alignment. Inother embodiments, good alignment may be considered to be a differentarrangement of the coil arrangements, depending on the layout andgeometry of the coil arrangements.

Compared to the coil arrangements of FIG. 3, the coil arrangements ofthe embodiment shown in FIG. 7 provide advantages for wireless powertransfer systems. For example, the receiver coil arrangement 702,typically mounted on an electric vehicle, is relatively simple,comprising a single planar coil 705. This reduces the cost andcomplexity of the IPT components on the electric vehicle. While theremay be more complexity on the transmitter side of the system as aresult, for example arising from the need to control the currents in thetransmitter coils 703 a, 703 b, and 704, this may be acceptable in somesituations in view of the advantages on the receiver side of the system.

In addition, the use of multiple coils in the transmitter device asshown in FIG. 7, and in transmitter devices according to embodimentsdiscussed herein, allows the currents in the transmitter coilarrangements to be controlled to increase power transfer efficiency.When both transmitter coil structures 703 a-b and 704 are coupled to thereceiver coil structure 702, the magnitude of current in the transmittercoils 703 a, 703 b and 704 can be adjusted to increase efficiency for agiven output power. For example, if the coupling from transmitter coilstructure 703 a and 703 b and transmitter coil structure 704 is equal,high efficiency can be achieved by running equal currents through thetwo transmitter coil arrangements to reduce resistive losses. However,if one of the transmitter coil arrangements 703 a-b or 704 has a verylow coupling it may be more efficient to zero the current in that coilarrangement.

FIG. 8 is a diagram illustrative of the spatial distribution of powercontributions of the coils shown in FIG. 7 during wireless powertransfer. In a similar manner to FIG. 4, FIG. 8 depicts in plan view thearea 800 covered by the coils 700 of FIG. 7. Areas 801 and 802 outlinedin a broken line indicate the exemplary approximate spatial distributionof the power contribution from the co-planar transmitter coils 703 a and703 b of coil structure 701 to the receiver coil 705 shown in FIG. 7.Area 803 outlined in a solid line depicts the exemplary approximatespatial distribution of the power contribution from the singletransmitter coil 704 to the receiver coil 705. Line 804 shown in boldrepresents the estimated tolerance region for power transfer above acertain threshold level for the coil arrangements shown in FIG. 7.

Compared to the estimated tolerance region of the coils shown in FIG. 4,the tolerance region 804 of coils 700 is wider in the direction parallelto a line between the centers of co-planar coils 703 a and 703 b, butnarrower in the direction perpendicular to a line between the centers ofco-planar coils 703 a and 703 b. As mentioned above, if we assume theview in FIG. 7 is looking forward with respect to an electric vehicle,this makes coil arrangements 700 more tolerant to transversemisalignment of the vehicle but less tolerant to longitudinalmisalignment when compared to the system of FIG. 3. As has beendiscussed above, such tolerances may be desirable in certain situations,for example where the electric vehicle is controlled by a control systemto automatically position the vehicle over the transmitter device.

It will be appreciated that the coils of FIG. 7, as well as other coilarrangements within the scope of various embodiments, may be mounted onthe ground and on an electric vehicle in any orientation. That is, thecoil arrangements may be configured such that the longitudinal directiondepicted in FIG. 6 and FIG. 7 is the transverse direction and viceversa. Those of skill in the art will appreciate that the exemplaryorientations discussed herein are not limiting to various embodimentsand coil arrangements according to various embodiments may be used inalternative orientations, in which case any advantages of the coilarrangements discussed herein relating to a particular direction willapply equally to the same direction relative to the alternativeorientation of the coil arrangements.

FIG. 9 is a perspective view illustration of induction coils 900 in awireless power transfer system according to an exemplary embodiment.Coils 900 comprise transmitter coil structures 901 and 904 that aresimilar to the transmitter coil structures of FIG. 5 and FIG. 7 andinclude co-planar coils 903 a and 903 b in the first transmitter coilstructure 901, and single transmitter coil 904. In the embodiment shownin FIG. 9, the receiver coil structure 902 comprises two co-planarreceiver coils 905 a and 905 b.

The embodiment shown in FIG. 9 possesses the advantages discussed aboveof using a transmitter device having multiple transmitter coils with areceiver device having a single receiver coil arrangement, the singlereceiver coil structure 902 in the embodiment of FIG. 9 comprising twoco-planar coils 905 a and 905 b. The receiver device in FIG. 9 may haveadditional coil as compared to the coils of FIG. 7 and therefore moreelectrically conducting material, typically Litz wire, may be used.

FIG. 10 is a diagram illustrative of the spatial distribution of powercontributions of the coils 900 shown in FIG. 9 during wireless powertransfer. Similarly to FIG. 8, the approximate areas 1001 and 1002 ofpower contribution of the single transmitter coil 904 to the co-planarreceiver coils 905 a and 905 b are shown by solid lines and theapproximate area 1003 of power contribution of the two co-planartransmitter coils 903 a and 903 b is shown outlined in a dotted line. Itshould be noted that, compared to the areas of power contribution ofFIG. 8, the positions of the contributions from the transmitter coilarrangements are reversed, i.e. in FIG. 8 the single transmitter coil704 contributes power to the receiver coil centrally within area 800while in FIG. 10 it is the co-planar transmitter coils 903 a and 903 bthat contribute power to the receiver coil centrally within area 1000.The same reversal is true for the transmitter coils contributing to theperipheral power contribution regions in these figures.

Compared to the estimated tolerance region 404 of the coils shown inFIG. 4, the tolerance region 1004 of coil arrangements 900 is againwider in the transverse direction with respect to the electric vehicle.Therefore the coils 900 of FIG. 9 may be again more suited tocircumstances requiring increased transverse misalignment tolerance thanthe coil arrangements shown in FIG. 3. Compared to the estimatedtolerance region 804 of the coil arrangements shown in FIG. 7, thetolerance region 1004 shown in FIG. 10 is wider in the longitudinaldirection. Since the widths of the tolerance regions are similar, theoverall tolerance to misalignment of the coil arrangements shown in FIG.9 is greater than those shown in FIG. 7. Therefore these coilarrangements 900 may be desirable where a larger overall degree oftolerance to misalignment is sought.

Furthermore, compared to the coils shown in FIG. 3, the coupling betweenthe transmitter and receiver coils 901 and 902 in the embodiment shownin FIG. 9 is higher in the longitudinal direction. For any givenalignment, this allows for less magnetic field emissions from the sideof the coils.

FIG. 11 is a perspective view illustration of induction coils in awireless power transfer system 1100 according to an exemplaryembodiment. Again, transmitter coil structures 1103 a-b and 1104 aresimilar to the coil structures 501 and 502 shown in FIG. 5. In theembodiment shown in FIG. 11, receiver coil structures 1102 and 1106 alsocomprise coil structures comprising two co-planar receiver coils 1105 aand 1105 b for the coil structure 1102 and a single receiver coil 1106.

The embodiment shown in FIG. 11 has a receiver device comprising coilstructures similar to that of the coil structures shown in FIG. 3. As aresult, the embodiment of FIG. 11 may not realize at least some of thebenefits as described with reference to FIG. 7 and FIG. 9. In fact, thecost and complexity of the coil arrangements may be higher as comparedto other embodiments on both the transmitter and receiver sides of theIPT system. However, the embodiment shown in FIG. 11 may possess otherbenefits that may be desirable in certain circumstances.

For example, the embodiment shown in FIG. 11 may able to achieve higherpower transfer rates between the transmitter and receiver coils 1101 and1102 for a given transmitter current on account of the greater number ofcoils in the system. This may enable coils of FIG. 11 to be used totransfer power at a higher rate as compared to the embodimentspreviously described or at the same rate but using a lower transmitteror base device current. A reduction in the current in the transmitterdevice may be desirable for reducing the magnetic field emissions fromthe wireless power transfer system. The amount of magnetic fieldemissions from the side of the coils is approximately proportional tothe current in the transmitter device, therefore the lower thetransmitter device current, the lower the field emissions.

FIG. 12 is a diagram illustrative of the spatial distribution of powercontributions of the coils shown in FIG. 11 during wireless powertransfer. The areas outlined by solid lines 1201, 1202 and 1203approximate the area of power contribution from the single transmittercoil 1104 across the area 1200 of the coils 1100 while the areasoutlined by dotted lines 1204, 1205 and 1206 are approximations of thespatial power contributions from the co-planar transmitter coils 1103 aand 1103 b. The dotted shaded areas show the power contributions assupplied to the single receiver coil 1106 while the diagonally shadedareas show the power contributions as supplied to the co-planar receivercoils 1105 a and 1105 b. Essentially, the power contributions of coils1100 are the sum of the power contributions of the coils 700 of FIG. 7and coils 900 of FIG. 9.

Bold line 1207 represents the region of tolerance to misalignment of thetransmitter and receiver coils 1101 and 1102 for the coil arrangementsof FIG. 11. This region is larger than the tolerance regions for thecoil arrangements of FIG. 3, FIG. 7, and FIG. 9 in both the transverseand longitudinal directions. Therefore the coil arrangements of FIG. 11are overall more tolerant to misalignment between the coils and may beuseful where such a level of tolerance is desired.

FIG. 13 is a perspective view illustration of induction coils 1300 in awireless power transfer system according to an exemplary embodiment. InFIG. 13, the transmitter coil structures 1301 and 1304 are similar tothe coil structures 601 and 602 shown in FIG. 6, respectively. Thereceiver coil structures 1302 and 1306 are similar to the receiver coilstructures 1102 and 1106 of FIG. 11, comprising two co-planar receivercoils 1305 a and 1305 b and a single receiver coil 1306.

Similarly to the coils 1100 of FIG. 11, coils 1300 may result in anincreased power transfer rate between the transmitter and receiverdevices of an IPT system. Again, this can allow faster power transfer orlower currents for a given power transfer and therefore reduced strainon the system components and reduced magnetic field emissions. Coilarrangements 1300 may involve some increased costs and complexity insome cases on the vehicle side of the system, and a larger single coil1304 compared to the single coil 1104 of the embodiment shown in FIG.11, which may require more wound conducting material and thereforegreater weight and cost.

FIG. 14 is a diagram illustrative of the spatial distribution of powercontributions of the coils 1301 and 1302 shown in FIG. 13 duringwireless power transfer. As can be seen in relation to FIG. 14, themisalignment tolerance region of the coils 1300 is larger than that ofcoils 1100 of FIG. 11. The areas outlined by solid lines 1401, 1402 and1403 approximate the area of power contribution from the singletransmitter coil 1304 across the area 1400 of the coils 1300 while theareas outlined by dotted lines 1404, 1405 and 1406 are approximations ofthe spatial power contributions from the co-planar transmitter coils1303 a and 1303 b. The dotted shaded areas show the power contributionsas supplied to the single receiver coil 1306 while the diagonally shadedareas show the power contributions as supplied to the co-planar receivercoils 1305 a and 1305 b. The bold line 1407 is an approximation of aregion of misalignment tolerance between the transmitter and receivercoils 1301 and 1302.

Compared to the equivalent power contribution diagram of FIG. 12, it canbe seen that the spatial distribution of power contributions from coils1300 are wider in the transverse direction on account of the widerdimension of the single transmitter coil 1304. As a result, the coils1300 of FIG. 13 have greater tolerance to misalignment in the transversedirection than those discussed previously.

FIG. 15 is a perspective view illustration of induction coils 1500 in awireless power transfer system according to a further exemplaryembodiment. In FIG. 15, both the transmitter coil structures 1501 and1504 and receiver coil structures 1502 (formed of coils 1505 a and 1505b) are similar to the receiver coil structures of FIG. 11 with theco-planar receiver coils 1505 a and 1505 b collectively positionedsubstantially central to single receiver coil 1506. Stated another way,the receiver apparatus includes a first conductive structure 1502(including 1505 and 1505 b) configured to wirelessly receive power via amagnetic field generated by a transmitter conductive structure (1501 or1504 or both) having a length greater than a width. The first conductivestructure 1502 has a length greater than a width and includes a firstloop 1505 a and a second loop 1505 b enclosing a first area and a secondarea respectively. The first loop 1505 a and the second loop 1505 b havelower surfaces that are substantially coplanar. The first conductivestructure has a first edge and a second edge each intersecting a firstgeometric line running along a length of the first conductive structure1502. A second geometric line along the width of that runs between thefirst and second loops 1505 a and 1505 b is substantially perpendiculara line running along the length. The receiver apparatus further includesa second conductive structure 1506 configured to wirelessly receivepower via the magnetic field from the transmitter conductive structure1501. The second conductive structure 1506 encloses a third area and hasa length greater than a width. The first geometric line runs along thelength of the second conductive structure 1506. In some embodiments, acenter of the third area enclosed by the second conductive structure1506 is positioned substantially over a point between the first loop1505 a and the second loop 1505 b.

As shown in FIG. 15, the receiver coil structures 1502 and 1506, whichmay be electrically connected or connectable to a load such as anelectric vehicle battery, are arranged in a different orientation wheninterfaced with the transmitter coil structures 1501 (including coils1503 a and 1503 b) and 1504, being rotated through substantially 90° inthe horizontal plane compared to the receiver coils of FIG. 11 so thatthe co-planar receiver coils 1505 a and 1505 b are substantiallyperpendicular to the co-planar transmitter coils 1503 a and 1503 b. Thatis, the longitudinal axis of the receiver coils is generallyperpendicular to the longitudinal axis of the transmitter coils 1503 aand 1503 b of the transmitter conductive structure 1501. Stated anotherway, a line between the centers of the co-planar receiver coils 1505 aand 1505 b is substantially perpendicular to a line between the centersof the co-planar transmitter coils 1503 a and 1503 b. Stated yet anotherway, the first geometric line described above running along the lengthof the second conductive structure is substantially perpendicular to athird geometric line running along the length of the transmitterconductive structure 1501.

It should be appreciated that the first and second loops 1505 a and 1505b may be either a single coil wound to enclose the first and secondareas, or, in another embodiment, be formed of different separate coils1505 a and 1505 b to enclose the first and second areas. In fact, itshould be appreciated that in any of the figures as described aboveshowing co-planar structures, the two separate co-planar structures maybe formed by either a single coil wound to enclose the first and secondareas, or, be formed of separate coils to enclose the first and secondareas Moreover, the first receiver conductive structure 1502 and thesecond receiver conductive structure 1506 may be positioned to maintaina substantial absence of mutual coupling between the first receiverconductive structure 1502 and the second receiver conductive structure1506 as explained above.

The embodiment of FIG. 15 shares some of the advantages anddisadvantages discussed above in relation to the embodiments shown inFIG. 11 and FIG. 1. However, the tolerance to misalignment in differentdirections has different characteristics, as will now be discussed inrelation to FIG. 16, which is a diagram illustrative of the spatialdistribution of power contributions of the coils shown in FIG. 15 duringwireless power transfer. The areas outlined by solid lines 1601, 1602and 1603 approximate the area of power contribution from the singletransmitter coil 1504 across the area 1600 of the coils 1500 while theareas outlined by dotted lines 1604 to 1609 are approximations of thespatial power contributions from the co-planar transmitter coils 1503 aand 1503 b. The dotted shaded areas show the power contributions assupplied to the single receiver coil 1506 while the diagonally shadedareas show the power contributions as supplied to the co-planar receivercoils 1505 a and 1505 b. The bold line 1610 is an approximation of aregion of misalignment tolerance between the transmitter and receivercoils.

Comparison can be made between the spatial distribution of powercontributions shown in FIG. 16 with that shown in FIG. 12, which relatesto the embodiment shown in FIG. 11. The dotted areas, which depict thepower contributions supplied to the single receiver coil, are similarlydistributed in both cases. However, in FIG. 16, the diagonally shadedareas, which depict the power contributions supplied to the co-planarreceiver coils 1505 a and 1505 b, are situated along the top and bottomof area 1600. This contrasts to the equivalent regions in FIG. 12, whichare situated in the middle of area 1200.

The overall tolerance to misalignment shown in FIG. 16 is a larger areathan that of FIG. 12 and is also more rectangular in shape. Statedanother way, the first and second receiver coil structures 1502 and 1506collectively have a first center point (e.g., a center point of ageometric rectangle covering the surface area of the coil structures1505 a-b and 1506). The transmitter conductive structure 1502 a-b and1504 has a second center point (e.g., a center point of a geometricrectangle covering the surface area of the transmitter conductivestructure). A set of points defined by offset distances between thefirst and second center points, in which an amount of power transfer isabove a threshold is substantially rectangular. The effect of this is toreduce the dependency of the amount of tolerance to misalignment in afirst direction to the amount of misalignment in a directionperpendicular to the first direction. It can be seen from bold line 1610in FIG. 16 that, even if a vehicle is poorly aligned in the transversedirection, the degree of tolerance in the longitudinal direction islittle affected unless the transverse misalignment is significant (e.g.,approaching the borders of the region bounded by line 1610). This can becompared to the overall tolerance of the embodiment shown in FIG. 11,which is depicted by line 1207 in FIG. 12, in which the oval-shapednature of line 1207 indicates misalignment in the transverse directionreduces the degree of tolerance to misalignment in the longitudinaldirection, and vice versa.

As a result, in the embodiment shown in FIG. 15, misalignment in onedirection does not necessarily compound the chances of misalignment inthe other direction. It also allows manufacturers to design bothtransmitter and receiver coil arrangements to cater for the tolerancerequirements of a given system or situation independently in both thetransverse and longitudinal directions. This flexibility may simplifythe design of suitable coil arrangements.

The large tolerance to misalignment of the embodiment shown in FIG. 15compared to other embodiments described above may allow the size of thecoil arrangements to be decreased, thus maintaining a particular degreeof tolerance while also reducing component costs. A reduction in size ofthe coil arrangements may also reduce magnetic field emissions beyondthe boundaries of a vehicle.

A similar exemplary embodiment is shown in FIG. 17, which is aperspective view illustration of induction coils 1700 in a wirelesspower transfer system according to a still further exemplary embodiment.In FIG. 17, both the transmitter coil structures 1701 and 1704 andreceiver coil structures 1702 and 1706 are similar to the receiver coilsof FIG. 13, however the receiver coil structures 1702 and 1706 arearranged in a different orientation, being rotated through substantially90° in the horizontal plane compared to the receiver coil structures1302 and 1306 of FIG. 13 so that the co-planar receiver coils 1705 a and1705 b are substantially perpendicular to the co-planar transmittercoils 1703 a and 1703 b.

The embodiment of FIG. 17 shares many of the advantages anddisadvantages discussed above in relation to the embodiment of FIG. 15.Furthermore, it has similar characteristics of misalignment tolerance,as shown in FIG. 18, which is a diagram illustrative of the spatialdistribution of power contributions of the coils shown in FIG. 17 duringwireless power transfer. The areas outlined by solid lines 1801, 1802,and 1803 approximate the area of power contribution from the singletransmitter coil 1704 across the area 1800 of the coils 1700 while theareas outlined by dotted lines 1804 to 1809 are approximations of thespatial power contributions from the co-planar transmitter coils 1703 aand 1703 b. The dotted shaded areas show the power contributions assupplied to the single receiver coil 1706 while the diagonally shadedareas show the power contributions as supplied to the co-planar receivercoils 1705 a and 1705 b. The bold line 1810 is an approximation of aregion of misalignment tolerance between the transmitter and receivercoils.

The misalignment tolerance characteristics of the embodiment of FIG. 17are similar to those of the embodiment of FIG. 15 and described above inrelation to FIG. 16. However, the regions of power contribution from thesingle transmitter coil 1704, as depicted by areas 1801, 1802 and 1803,are larger than the equivalent regions in FIG. 18. This reflects thelarger size of the single transmitter coil 1704 compared to the singletransmitter coil 1504 in FIG. 15. As a result there is greater overlapbetween regions of power contribution from the different transmittercoils in FIG. 18 compared to FIG. 16. Therefore, in comparison to theembodiment of FIG. 15, the embodiment of FIG. 17 may provide a greaterrange of misalignment positions between the coil arrangements in whichmore than one of the transmitter and/or receiver coils aretransmitting/receiving power contributions. This may result in moreefficient power transfer in these positions and a system that may stillbe able to transfer power if one of the transmitter coil arrangementsmalfunctions.

In the embodiments of FIG. 15 and FIG. 17 the receiver coil structuresare substantially perpendicularly oriented relative to the transmittercoil structures. It is the relative orientation of the coil structuresthat is relevant and embodiments may be provided in which the receivercoil arrangements are mounted in a transverse orientation on theunderside of an electric vehicle (as shown in FIG. 15 and FIG. 17assuming the figures are viewed longitudinally relative to the vehicle),a longitudinal orientation, or any other orientation. It will also beappreciated that, for some arrangements of transmitter coils an electricvehicle having receiver coil structures mounted underneath may be ableto orient the receiver coils in any orientation relative to thetransmitter coils depending on the direction from which the vehicledrives over the transmitter coils and hence the orientation of thevehicle. Therefore the controller or driver of an electric vehicle mayhave a choice as to which way the transmitter and receiver coils areoriented during a charging operation. This choice may be dictated by thedesired characteristics of charging associated with the possibleorientations. However, some transmitter coil arrangements may be mountedon the ground such that a vehicle is practically only able to drive overit from one direction, for example in a parking space or garage.

More generally, at least some embodiments include receiver andtransmitter coil structures that are orientated such that the co-planarreceiver coils and co-planar transmitter coils do not couple, or have acoupling below a predetermined threshold, when the receiver andtransmitter coil structures are well aligned, for example when thephysical centers of receiver and transmitter coil arrangements arevertically aligned. The above description has described configurationsin which the level of coupling between the receiver and transmittercoils is very low when the coils are substantially perpendicularlyoriented, for example.

In other embodiments there may be provided transmitter coil structuressimilar to those shown in FIG. 15 and FIG. 17 without the singletransmitter coil 1504 or 1704. That is, the transmitter coilarrangements in these embodiments comprise only co-planar transmittercoils. It can be seen from FIG. 16 and FIG. 18 that if a receiver coilstructures such as is shown in the figures is aligned centrally withsuch transmitter coil structures then there may be lower rates of powertransfer than could be achievable if the single transmitter coil waspresent.

Referring again to the coils 600 of FIG. 6, the direction of the currentin the coil arrangements may be controlled in order to increase powertransfer efficiency and reduce some negative effects as will now bedescribed and as will be further described below.

In an embodiment, the currents in the co-planar transmitter coils 601 aand 601 b may be configured to flow in opposite directions such that thecurrents in adjacent portions of co-planar transmitter coils 601 a and601 b flow in the same direction. For example, the current in coil 601 amay flow clockwise while the current in coil 601 b flowscounterclockwise, or vice versa. For a given flow direction of thecurrents in the co-planar transmitter coils 601 a and 601 b, the currentin the single large transmitter coil 602 can flow in one of twodirections, either clockwise or counterclockwise, i.e. either in thesame direction as the current in coil 601 a or in the same direction asthe current in coil 601 b. If the current in the single coil 602 flowsin the same direction as coil 601 a, then the magnetic flux fieldproduced by the transmitter coil arrangements 600 will be offset fromthe center of the coil arrangements in the direction of coil 601 a.Equally, the magnetic flux field will be offset in the direction of coil601 b if the current in the single coil 602 flows in the same directionas coil 601 b. Therefore, by changing the direction in which the currentflows in either the single transmitter coil 602 or in the co-planartransmitter coils 601 a and 601 b, the position of the strongestmagnetic flux density can be varied.

The same consideration applies to the direction of currents in thetransmitter coils 500 of FIG. 5 and other coils within the scope ofvarious embodiments, although the amount of offset of the magnetic fieldas a consequence of switching the current in either the co-planar coils501 a and 501 b or the single coil 502 may be less than that of the coilarrangements of FIG. 6 because the edges of the coil arrangements arenot as aligned.

During wireless power transfer in a wireless power transfer system, ifthe receiver coil arrangements are misaligned with the transmitter coilarrangements then the direction of currents in the coils can becontrolled to offset the position of the region of greatest magneticfield strength to increase the level of coupling between the transmitterand receiver coils and therefore increase the efficiency of wirelesspower transfer. To that end, the wireless power transfer system maycomprise a mechanism operable to detect the position of the receiverdevice in relation to the transmitter device. An exemplary positiondetection mechanism will be discussed further below. Furthermore, thesystem may comprise a mechanism for controlling the current in either orboth of the co-planar coil arrangement or single coil arrangement of thetransmitter device based on the detected positions of the transmitterand receiver devices. The control mechanism may be comprised in thetransmitter device in an embodiment.

The control mechanism may be operable to alter the direction of currentin one or both of said coils in response to the position of the receivercoil arrangements in relation to the transmitter coils as identified bythe position detection mechanism. For example, if a receiver coil ismisaligned transversely in the direction of transmitter coil 601 a asshown in FIG. 6, the control mechanism may cause the current in thesingle coil 602 to flow in the same direction as the current in thetransmitter coil 601 a, which could be either clockwise orcounterclockwise. This causes the generated magnetic field to be offsettransversely in the direction of transmitter coil 601 a thereforedirecting the magnetic field generally towards the receiver coils. In analternative example, the direction of current in the co-planar coils maybe altered. In these examples, the currents in the coils are controlledsuch that the current in whichever co-planar coil 601 is nearest themisaligned receiver device flows in the same direction as the current inthe single coil 602.

If the transmitter and receiver coils are well aligned it may be moreefficient not to offset the region of highest magnetic field strengthgenerated by the transmitter coils. If the transverse alignment of thetransmitter and receiver coil arrangements is detected to be within acertain predefined threshold by the position detection mechanism thenthe control mechanism may be operable to zero the current flowing ineither the co-planar transmitter coils 601 a and 601 b or the singlecoil 602 such that the generated magnetic field is centralized over thetransmitter coil structures and aligned better with the receiver coilsthan if the field was offset.

In another embodiment, the wireless power transfer system may be able todetermine the relative orientations of the wireless power receiverdevice and the wireless power transmitter device. A mechanism fordetermining the relative orientations of the receiver and transmitterdevices may be provided in addition to the position detection mechanismin some embodiments. Based on the determined relative orientationsand/or the relative positions of the wireless power receiver device andthe wireless power transmitter device, a current supply mechanism maysupply current to the transmitter coils accordingly, for example toincrease power transfer rates or efficiency.

There will now be described an example with reference to the embodimentshown in FIG. 17.

In the positions shown in FIG. 17, the receiver coil structures 1702 and1706 may be considered well aligned with the transmitter coil structures1701 and 1704 since the centers of each coil arrangement are inapproximate vertical alignment. Referring to the spatial distribution ofpower contributions shown in FIG. 18, the most significant contributionof power to the middle section of area 1800 in the transverse directionis from the single transmitter coil 1704, as shown by areas 1801, 1802and 1803. Therefore if the transmitter and receiver coil arrangementsare in this alignment position, and if the coil arrangements areperpendicularly oriented to each other, it may be beneficial to supplycurrent to the single transmitter coil 1704 only. Supplying current, andtherefore power, to the co-planar transmitter coils 1703 a and 1703 b inthis case may result in little of that power being transferred to thereceiver coils, which may be inefficient in some cases. Zeroing thecurrent to the co-planar transmitter coils may also avoid an asymmetricmagnetic field being produced, which again may reduce power transferefficiency in some cases.

If however, the receiver coil arrangements 1702 are misalignedtransversely relative to the transmitter coil arrangements 1701, forexample misaligned in the direction of the co-planar transmitter coil1703 a, more efficient power transfer may be achievable by supplyingcurrent to the transmitter coils differently. FIG. 18 shows thatsignificant contribution of power to regions near the transverse edgesof area 1800 comes from the co-planar transmitter coils 1703 a and 1703b, as shown by areas 1804-1809. Therefore, misalignment towards thetransverse edge of area 1800 may mean supplying current to just theco-planar transmitter coils 1703 a and 1703 b, and zeroing the currentsupplied to the single transmitter coil 1704 provides increased powertransfer efficiency. Alternatively, the direction of the current in thetransmitter coil 1703 a nearest to the receiver coil arrangements may becontrolled to be the same as that in the single transmitter coil 1704,as discussed above.

Therefore, the determination of both the relative orientations of thetransmitter and receiver coil arrangements, as well as their relativepositions, may be used to control how current is supplied to thetransmitter coils.

Any appropriate system or method may be used to determine the relevantpositions and orientations of the receiver and transmitter devices.

FIG. 19 is a schematic view of induction coils in a wireless powertransfer system 1900 according to an exemplary embodiment. The coils maybe configured in any of the configurations as described above withreference to FIGS. 3-18.

The system 1900 comprises transmitter or “primary” coil structure 1901,and receiver or “secondary” coil structure 1902, as generallyillustrated by the coil configurations as described above.

The primary coil structure 1901 may comprise first primary coilstructure 1903 having an associated inductance L₁, and a second primarycoil structure 1904 having an associated inductance L₂. The secondarycoil structure 1902 may have an associated inductance L₃.

In operation, as generally described with reference to FIG. 2, power isdelivered to the first primary coil structure 1903 with a currentI_(L1), and to the second primary coil structure 1904 with a currentI_(L2). A magnetic field is emitted as a result, which induces a voltagecausing a current I_(L3) to pass through the secondary coil structure1902.

Each of the first and second primary coil structures 1903 and 1904 iscoupled with the secondary coil structure 1902. The coupling coefficientbetween the first primary coil structure 1903 and the secondary coilstructure 1902 may herein be referred to as “k₁₃,” while couplingcoefficient between the second primary coil structure 1904 and thesecondary coil structure 1902 may herein be referred to as “k₂₃.”

The coupling coefficients may be determined by any suitable mechanism.In an exemplary embodiment, the receiver side, for example electricvehicle charging system 214 of FIG. 2, may comprise a mechanism formeasuring the short circuit current across the secondary coil structure1902. This can be measured by selectively closing switches in asub-circuit. For a given base current (or currents) in the primary coilstructure, the short circuit current across the secondary inductor isindicative of the level of coupling between them. Any appropriatemechanism of measuring the short circuit current may be used.

In some embodiments, particularly in a series tuned system, open circuitvoltage may be measured and used to determine coupling. It should beappreciated that measurement of short circuit current or open circuitvoltage will be dependent on the tuning topology. If tuning is such thata current source output is presented, for example as in parallel tuning,short circuit current will need to be measured as the circuit cannot beopened. Conversely, if a voltage source output is presented, such as inseries tuning, open circuit voltage will be required in order todetermine the coupling coefficient.

It should be appreciated that the mechanism for measuring voltage andmechanism for measuring current may be distinct devices in communicationwith one or more devices of a wireless power transfer system, orintegrated into said devices.

In order to determine the coupling coefficient between each of theprimary and secondary coil structures 1901 and 1902, power may besupplied to each of the primary coil structures 1903 and 1904, and/orcombinations thereof, in a sequence, and measurements of the individualcontributions to power induced in the secondary coil structure 1902made. For example, power may be supplied to only the first primary coilstructure 1903 only for a certain number of milliseconds (e.g., 250milliseconds), and the resulting current and/or voltage of power inducedin the secondary coil structure 1902 measured. Power may then besupplied to only the second primary coil structure 1903 for a certainnumber of milliseconds (e.g., 250 milliseconds), and the resultingcurrent and/or voltage of power induced in the secondary coil structure1902 measured. Power may then be supplied to both of the primary coilstructures 1903 and 1904 run together for a certain number ofmilliseconds (e.g., 250 milliseconds) and the resulting current and/orvoltage of power induced in the secondary coil structure 1902 measured.From these current and/or voltage measurements, coupling coefficientsbetween each of the primary and secondary coils 1901 and 1902 may bedetermined.

Once the coupling coefficients have been determined, the contributionsof each primary coil structure 1903 and 1904 to each secondary coilstructure 1902 may be used to determine the magnitudes and/or relativephases of currents I_(L1) and I_(L2) to be applied in the transmissionor primary coils 1901. In exemplary embodiments, determination of thecoupling coefficients and/or determination of control parameters forcurrents I_(L1) and I_(L2) may be performed only once at the time ofinitial alignment of the transmitter and receiver sides, periodically,in real time according to detected changes in power transfercharacteristics, or on communication between the transmitter andreceiver sides. In addition, the magnitude and/or relative phases ofcurrents I_(L1) and I_(L2) are controlled to reduce emissions from thesystem 1900 and to maintain emissions below a threshold.

It should be appreciated that application of the exemplary scenariosoutlined below may be heavily influenced by the configuration of aparticular system, and the objectives of the system designer—for examplewith regard to minimizing losses or reducing stress on components withinthe system.

The higher the coupling coefficient is between a transmitter device anda receiver device, the more efficient power transfer will be whenwirelessly transmitting power from the transmitter device to thereceiver device. Therefore, the value of the measured coefficients maybe used as an input in determining the magnitudes of the currents I_(L1)and I_(L2) to be applied. For example, where k₁₃>k₂₃, the magnitude ofI_(L1) may be increased relative to I_(L2) (or the second primary coilstructure 1904 completely turned off) in order to take advantage of thecloser coupling and transfer power more efficiently. While large changesin current in the primary coil structure 1901 may be generallyundesirable due to stresses on the power supply or supplies, some degreeof variability may be tolerated without adversely impacting theefficiency of the system.

Further, power delivery through certain coil structures may beprioritized in order to utilize generally more efficient operation ofcertain coil types. For example, increasing the current through thesubstantially co-planar transmitter coils 601 a and 601 b of FIG. 6 maybe prioritized over the current through the single planar transmittercoil 604.

In an exemplary embodiment, it may be preferable to balance themagnitude of both currents to be as similar as possible in order toreduce losses.

In another exemplary embodiment, it may be desirable to determine aconstant ratio of the magnitudes of the currents according to the knownrelative losses (for example resistive losses) in each primary coil. Indoing so, the current magnitude may be controlled such that the lossesare balanced in each coil arrangement.

In exemplary embodiments, the phase of the currents I_(L1) and I_(L2)may be controlled in addition to, or in place of, the magnitude of saidcurrents. Both the phase of the currents and the magnitude may beadjusted simultaneously. The voltages V_(oc13) and V_(oc23) induced inthe secondary coil structure 1902 as the result of magnetic fieldsemitted by the first and second primary coil structures 1903 and 1904respectively may be given by the equations:V _(oc13) =ωk ₁₃√{square root over (L ₁ L ₃)}I _(L1) sin(ωt); andV _(oc23) =ωk ₂₃√{square root over (L ₂ L ₃)}I _(L2) sin(ωt+A),

where L₁ is the inductance of the first primary coil structure 1903, L₂is the inductance of the first primary coil structure 1904, and A is thephase difference between currents I_(L1) and I_(L2).

The phase differential may be controlled, for example, in order to tuneor detune the system in order to achieve desirable system conditions.Current I_(L3) may be determined by the following equation:

$I_{L\; 3} = \frac{( {R - {j\; X}} )( {V_{{oc}\; 13} + {V_{{oc}\; 23}{\cos(A)}} + {j\; V_{{oc}\; 23}{\sin(A)}}} )}{X^{2}}$

where R is the resistance of the secondary coil arrangement 1902, and Xis the reactance of same.

The following equations may be used to determine the relative amounts ofVAR and real load onto the power supply, normalized relative toreactance in order to allow application of the results of the equationsto any receiver comprising a secondary coil structure regardless ofinductance:

$\frac{Z_{r\; 13}}{X} = \frac{V_{{oc}\; 13}}{( {Q - j} )( {V_{{oc}\; 13} + {V_{{oc}\; 23}{\cos(A)}} + {j\; V_{{oc}\; 23}{\sin(A)}}} )}$$\frac{Z_{r\; 23}}{X} = \frac{{V_{{oc}\; 23}{\cos(A)}} + {j\; V_{{oc}\; 23}{\sin(A)}}}{( {Q - j} )( {V_{{oc}\; 13} + {V_{{oc}\; 23}{\cos(A)}} + {j\; V_{{oc}\; 23}{\sin(A)}}} )}$In an embodiment, the phase of the currents between the two primary coilstructures 1903 and 1904 is one of either zero degrees or 180 degrees.The particular phase difference, either 0 or 180 degrees, depends on theposition of the secondary coil relative to each of the two primary coils1901.

FIG. 20 is a graph 2000 illustrating the real and imaginary componentsof the impedance seen at the secondary coil structure 1902 of FIG. 19,plotting normalized impedance against phase difference A betweencurrents I_(L1) and I_(L2) Trace 2001 and trace 2002 are the real andimaginary loads seen by V_(oc13), while trace 2003 and trace 2004 arethe real and imaginary loads seen by V_(oc23).

In exemplary embodiments the phase difference may be controlled to bewithin −0.5<A<0.5. In doing so, tuning of the system by way of relativephase as described above may be achieved without causing stresses on thepower supply which may otherwise negate the benefits of tuning.

FIGS. 21A, 21B, and 21C illustrate the effects of phase difference oncurrent and voltage. FIG. 21A is a vector diagram illustrating anexemplary scenario in which currents I_(L1) and I_(L2) have the samephase. The phase difference between the voltages V_(oc13) and V_(oc23),and the current I_(L3) is a natural result of parallel tuning.

FIG. 21B is a vector diagram illustrating an exemplary scenario in whichI_(L1) leads I_(L2). The resulting voltage seen by the system(V_(ocsum)) may be reduced in comparison with that of FIG. 21A. This mayreduce the inductance at the primary coil structure 1901. Thisadjustment in inductance may be used to tune the system 1900 to improvecoupling. It is envisaged that if the phase difference is too great oneprimary coil structure may be capacitive and the other inductive, whichcould detune the two coil structures in opposite directions. This mayreduce efficiency in the components supplying power to the coilarrangements—for example an H-bridge being used in an inverter—which maybe required to drive the extra VAR load, or even cause failure if thisload was too large. As discussed previously, it is envisaged that thesystem may be operated within a limited range with regard to phasedifference in order to reduce these effects.

FIG. 21C is a vector diagram illustrating an exemplary scenario in whichcurrents I_(L1) and I_(L2) are substantially antiphase, such that thevoltages V_(oc13) and V_(oc23) oppose each other to result in aV_(ocsum) less than individual coil arrangement contributions. Theresulting reduction in I_(L3) and V_(ocsum) may lead to a reduced powerdemand on the transmitter.

Due to the reduced power demands, the conduction angle of any invertersassociated with the power supply may be higher. This indicates that thetime over which power is conducted is increased, reducing the peakcurrents and associated stress borne by the components.

There will now be described, with reference to FIG. 22, components of awireless power transfer system. Any of the embodiments described abovemay use one or more of the components described with reference to FIG.22. For example, embodiments using the components of FIG. 22 inconjunction with that described above may provide for identifyingrelative positions and orientations of the receiver and transmitterdevices. An embodiment further comprises a control mechanism operable tocontrol the current in the transmitter coils based on the results of theposition and/or orientation determinations (e.g., a controller). Thecontrol mechanism may comprise a processor operable to determine anappropriate current supply configuration based on the detectedpositions/orientations of the transmitter and receiver coilarrangements.

FIG. 22 is a functional block diagram showing exemplary core andancillary components of the wireless power transfer system 100 ofFIG. 1. The wireless power transfer system 2210 illustrates acommunication link 2276, a guidance link 2266, and alignment systems2252, 2254 for the base system induction coil 2208 and electric vehicleinduction coil 2216. The base system induction coil 2208 may be formedfrom any of the embodiments of the transmitter coil configurationsdescribed above with reference to FIGS. 3-21. The electric vehicleinduction coil 2216 may be formed from any of the embodiments of thereceiver coil configurations described above with reference to FIGS.3-21. As described above with reference to FIG. 2, and assuming energyflow towards the electric vehicle 112, in FIG. 22 a base charging systempower interface 2254 may be configured to provide power to a chargingsystem power converter 2236 from a power source, such as an AC or DCpower supply 126. The base charging system power converter 2236 mayreceive AC or DC power from the base charging system power interface2254 to excite the base system induction coil 2208 at or near itsresonant frequency. The electric vehicle induction coil 2216, when inthe near field coupling-mode region, may receive energy from the nearfield coupling mode region to oscillate at or near the resonantfrequency. The electric vehicle power converter 2238 converts theoscillating signal from the electric vehicle induction coil 2216 to apower signal suitable for charging a battery via the electric vehiclepower interface.

The base wireless charging system 2212 includes a base charging systemcontroller 2242 and the electric vehicle charging system 2214 includesan electric vehicle controller 2244. The base charging system controller2242 may include a base charging system communication interface 162 toother systems (not shown) such as, for example, a computer, and a powerdistribution center, or a smart power grid. The electric vehiclecontroller 2244 may include an electric vehicle communication interfaceto other systems (not shown) such as, for example, an on-board computeron the vehicle, other battery charging controller, other electronicsystems within the vehicles, and remote electronic systems.

The base charging system controller 2242 and electric vehicle controller2244 may include subsystems or modules for specific application withseparate communication channels. These communications channels may beseparate physical channels or separate logical channels. As non-limitingexamples, a base charging alignment system 2252 may communicate with anelectric vehicle alignment system 2254 through a communication link 2276to provide a feedback mechanism for more closely aligning the basesystem induction coil 2208 and electric vehicle induction coil 2216,either autonomously or with operator assistance. Similarly, a basecharging guidance system 2262 may communicate with an electric vehicleguidance system 2264 through a guidance link to provide a feedbackmechanism to guide an operator in aligning the base system inductioncoil 2208 and electric vehicle induction coil 2216. In addition, theremay be separate general-purpose communication links (e.g., channels)supported by base charging communication system 2272 and electricvehicle communication system 2274 for communicating other informationbetween the base wireless power charging system 2212 and the electricvehicle charging system 2214. This information may include informationabout electric vehicle characteristics, battery characteristics,charging status, and power capabilities of both the base wireless powercharging system 2212 and the electric vehicle charging system 2214, aswell as maintenance and diagnostic data for the electric vehicle 112.These communication channels may be separate physical communicationchannels such as, for example, Bluetooth, zigbee, cellular, etc. Thesesystems may operate to determine and communicate the relative positionsand/or the relative orientations of the base system induction coil 2208and electric vehicle induction coil 2216 in any appropriate manner.

To communicate between a base wireless charging system 2212 and anelectric vehicle charging system 2214, the wireless power transfersystem 2210 may use both in-band signaling and an RF data modem (e.g.,Ethernet over radio in an unlicensed band). The out-of-bandcommunication may provide sufficient bandwidth for the allocation ofvalue-add services to the vehicle user/owner. A low depth amplitude orphase modulation of the wireless power carrier may serve as an in-bandsignaling system with minimal interference.

In addition, some communication may be performed via the wireless powerlink without using specific communications antennas. For example, thewireless power induction coils 2208 and 2216 may also be configured toact as wireless communication transmitters. Thus, some embodiments ofthe base wireless power charging system 2212 may include a controller(not shown) for enabling keying type protocol on the wireless powerpath. By keying the transmit power level (amplitude shift keying) atpredefined intervals with a predefined protocol, the receiver may detecta serial communication from the transmitter. The base charging systempower converter 2236 may include a load sensing circuit (not shown) fordetecting the presence or absence of active electric vehicle receiversin the vicinity of the near field generated by the base system inductioncoil 2208. By way of example, a load sensing circuit monitors thecurrent flowing to the power amplifier, which is affected by thepresence or absence of active receivers in the vicinity of the nearfield generated by base system induction coil 104 a. Detection ofchanges to the loading on the power amplifier may be monitored by thebase charging system controller 2242 for use in determining whether toenable the oscillator for transmitting energy, to communicate with anactive receiver, or a combination thereof.

To enable wireless high power transfer, some embodiments may beconfigured to transfer power at a frequency in the range from 10-60 kHz.This low frequency coupling may allow highly efficient power conversionthat may be achieved using solid state devices. In addition, there maybe less coexistence issues with radio systems compared to other bands.

FIG. 23 is a flow chart illustrating a method 2300 of operating awireless power transfer system according to an exemplary embodiment.Operation is described with reference to the components of FIG. 22.

At block 2301, a wireless power transfer system, such as wireless powertransfer system 2200, determines that power is to be wirelesslytransferred between a transmitter side such as the base wirelesscharging system 2209, and a receiver side such as the electric vehiclecharging system 2211. It should be appreciated that determining thatpower is to be transferred may be achieved in a variety of ways. Forexample, the electric vehicle controller 2212 may transmit a signalnotifying the base charging system controller 2210 of its presence inthe vicinity. In another exemplary embodiment, the base charging systemcontroller 2210 may monitor the load sensing circuit in order to detectthe presence or absence of active receivers in the vicinity as discussedabove. Similarly, this technique may be performed on the electricvehicle side.

In exemplary embodiments, additional information may be transferredbetween the transmitter and receiver sides as to desired operatingconditions. For example, electric vehicle controller 2212 may transmitdetails regarding the configuration of the electric vehicle chargingsystem 2211 to the base charging system controller 2210, and/orpreferred parameters for wireless power transfer. Such details mayenable losses on the receiver side, or the risk of unacceptable stresson components of the receiver, to be determined. This information may beused in determining control parameters for wireless power transfer—asdiscussed below.

On determining that power is to be transferred, at block 2302 thecontributions of each primary coil arrangement to wireless powertransfer to the secondary coil arrangement is measured. For example, thebase charging system controller 2210 may instruct the base chargingsystem power converter 2207 to supply power to the first primary coilarrangement 1903 for e.g., 250 milliseconds. During this period ameasurement is made of the short circuit current across the secondarycoil arrangement 1902 resulting from wireless power transfer, and/or theopen circuit voltage at same—depending on the tuning topology. This maybe repeated for the second primary coil arrangement 1904, and then bothof the primary coil arrangements simultaneously.

At block 2303 the measured voltage and/or current is transmitted to amechanism for determining coupling coefficients between each of theprimary coil arrangements 1903 and 1904, and at the secondary coilarrangement 1902 (e.g., a processor). For example, the voltage and/orcurrent may be measured by the electric vehicle power converter 2208 orseparate devices (not shown), and transmitted to the electric vehiclecontroller 2212. In other embodiments the voltage and/or currentmeasurements may be transmitted to the base charging system controller2210, whether directly from the mechanism for measuring the voltageand/or current through a communication link (such as between electricvehicle communication system 2216 and base charging communication system2215), or via an intermediary device such as the electric vehiclecontroller 2212.

At block 2304, the mechanism for determining coupling coefficients (forexample base charging system controller 2210 or electric vehiclecontroller 2212) uses the voltage and/or current measurements todetermine a coupling coefficient between each of the primary coilarrangements 1903 and 1904, and at the secondary coil arrangement 1902.

At block 2305, a mechanism for determining control parameters fordelivery of current to the primary coil arrangements 1903 and 1904 usesthe coupling coefficients to determine control parameters. Themechanisms for determining the control parameters may be any suitableprocessor—for example the base charging system controller 2210 or theelectric vehicle controller 2212.

The mechanism for determining the control parameters may do so based onthe coupling coefficients and known system parameters such as relativeresistance of the primary coil arrangements. Exemplary considerationsdictating the control parameters are discussed previously with referenceto FIG. 19, FIG. 20, FIG. 21A, FIG. 21B, and FIG. 21C.

Further, in exemplary embodiments the control parameters may be based atleast in part on the information relating to operation of the receiver,for example electric vehicle charging system 2211, as previouslydiscussed.

Further, in exemplary embodiments the control parameters may be based atleast in part on the desired operating conditions of the receiver, forexample electric vehicle charging system 2211. In other words, anelectric vehicle may be configured with desired operating conditions ofthe receiver. In some embodiments, determination of which controlparameters to use may comprise communication between the transmitter andreceiver systems to arrive at an agreement between the systems. In anexemplary embodiment, the electric vehicle charging system and the basewireless charging system 2209 may exchange information on theirpreferred parameters. In such an embodiment, the electric vehiclecharging system and the base wireless charging system 2209 may selectagreed upon parameters to operate—for example, the agreed parameters maybe selected based on the best (i.e., most optimal) conditions which bothare capable of operating at. Alternatively the agreed parameters may bebased on the lowest conditions which the electric vehicle is capable ofoperating at.

In some embodiments, achieving desired operating conditions at eitherthe receiver or transmitter may be prioritized. For example,conditioning the power received electric vehicle charging system 2211 toa desired current may be prioritized over efficiency of the basecharging system power converter 2207. It should be appreciated that thedetermination of the control parameters may be influenced by a largenumber of factors, and that the decision making may be highly dependenton design parameters for a particular wireless power transfer system.

At block 2306 a mechanism for delivering current to the primary coilarrangements 1903 and 1904, for example base charging system powerconverter 2207, is controlled according to the determined controlparameters. For example, the base charging system controller 2210 maydirectly control the magnitude and/or phase of the respective currentssupplied to the primary coil arrangements 1903 and 1904 by powerconverter 2207. In another embodiment the electric vehicle controller2212 may transmit desired control parameters to the base charging systemcontroller 2210 in order to indirectly control the power converter 2207.

The system may return to block 2302 periodically, or on determining thata change in the physical relationship between the primary and secondarycoil arrangements has occurred.

FIG. 24 is a flow chart of another exemplary method 2400 of operating awireless power transfer system, in accordance with an embodiment. Atblock 2402, a first magnetic field is generated via a first conductivestructure 501 (FIG. 5) in response to receiving a time-varying signalfrom a power source. At block 2404, a second magnetic field is generatedvia a second conductive structure 502 in response to receiving a secondtime-varying signal from the power source. The first and secondstructures are positioned to maintain a substantial absence of mutualcoupling between the first and second magnetic fields. In oneembodiment, the method 2400 may be performed by a base wireless powercharging system 202 (FIG. 2) that includes the coils 501 and 502 of FIG.5.

FIG. 25 is a functional block diagram of a wireless power transmitter2500, in accordance with an embodiment. The wireless power transmitter2500 may include means 2502 and 2504 for the various actions discussedwith respect to FIGS. 1-24.

FIG. 26 is a flow chart of another exemplary method 2600 of wirelesslyreceiving power, in accordance with an embodiment. At block 2602, poweris wirelessly received at a first conductive structure 1505 a-b (FIG.15), via a magnetic field generated by a transmitter conductivestructure 1501 having a length greater than a width. The firstconductive structure 1505 a-b has a length greater than a width. Thefirst conductive structure 1505 a-b includes a first loop 1505 a and asecond loop 1505 b enclosing a first area and a second area,respectively. The first loop 1505 a has a first lower surface and thesecond loop 1505 b has a second lower surface that are substantiallycoplanar. The first conductive structure 1505 a-b has a first edge and asecond edge each intersecting a first geometric line running along thelength of the first conductive structure 15051-b. At block 2604, poweris wirelessly received, at a second conductive structure 1506, via themagnetic field. The second conductive structure 1506 encloses a thirdarea and having a length greater than a width. The first geometric lineruns along the length of the second conductive structure 1506. The firstgeometric line is substantially perpendicular to a second geometric linerunning along the length of the transmitter conductive structure 1501.In one embodiment, the method 2600 may be performed by a base wirelesspower charging system 1500 (FIG. 2) that includes the coils 1502.

FIG. 27 is a functional block diagram of a wireless power receiver 2700,in accordance with an embodiment. The wireless power receiver 2700 mayinclude means 2702 and 2704 for the various actions discussed withrespect to FIGS. 1-26.

FIG. 28 is a flow chart of another exemplary method 2800 of operating awireless power transfer system, in accordance with an embodiment. Atblock 2802, a first magnetic field is generated via a first conductivestructure 501 (FIG. 5) based on a first current received from a powersource. At block 2804 a second magnetic field is generated via a secondconductive structure 502 based on a second current from the powersource. At block 2806, a respective coupling coefficient between each ofthe first and second conductive structures and a third conductivestructure configured to receive power via the first or the secondmagnetic field is determined. At block 2808, the first or second currentapplied to the first and second conductive structures is adjusted basedat least in part on the coupling coefficients. In one embodiment, themethod 2800 may be performed by a base wireless power charging system202 (FIG. 2) that includes the coils 501 and 502 of FIG. 5.

FIG. 29 is a functional block diagram of a wireless power transmitter2900, in accordance with an embodiment. The wireless power transmitter2900 may include means 2902, 2904, 2906, and 2908 for the variousactions discussed with respect to FIGS. 1-28.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations. Forexample, a means for generating may comprise a conductive structure. Ameans for applying electric current may comprise a power supply and thelike. A means for controlling may comprise a processor and the like.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. The described functionalitymay be implemented in varying ways for each particular application, butsuch implementation decisions should not be interpreted as causing adeparture from the scope of the embodiments of the invention.

The various illustrative blocks, modules, and circuits described inconnection with the embodiments disclosed herein may be implemented orperformed with a general purpose processor, a Digital Signal Processor(DSP), an Application Specific Integrated Circuit (ASIC), a FieldProgrammable Gate Array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm and functions described in connectionwith the embodiments disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. If implemented in software, the functions may bestored on or transmitted over as one or more instructions or code on atangible, non-transitory computer-readable medium. A software module mayreside in Random Access Memory (RAM), flash memory, Read Only Memory(ROM), Electrically Programmable ROM (EPROM), Electrically ErasableProgrammable ROM (EEPROM), registers, hard disk, a removable disk, a CDROM, or any other form of storage medium known in the art. A storagemedium is coupled to the processor such that the processor can readinformation from, and write information to, the storage medium. In thealternative, the storage medium may be integral to the processor. Diskand disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer readable media. The processor andthe storage medium may reside in an ASIC. The ASIC may reside in a userterminal. In the alternative, the processor and the storage medium mayreside as discrete components in a user terminal.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

Various modifications of the above described embodiments will be readilyapparent, and the generic principles defined herein may be applied toother embodiments without departing from the spirit or scope of theinvention. Thus, the present invention is not intended to be limited tothe embodiments shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. An apparatus for wirelessly transmitting power,the apparatus comprising: a first conductive structure configured togenerate a first magnetic field in response to receiving a firsttime-varying electrical current from a power source, the firstconductive structure comprising a first loop and a second loop enclosinga first area and a second area, respectively, the first loop having afirst surface and the second loop having a second surface that aresubstantially coplanar; and a second conductive structure configured togenerate a second magnetic field in response to receiving a secondtime-varying electrical current from the power source, the secondconductive structure comprising a third loop enclosing a third area, thefirst and second structures positioned to maintain a substantial absenceof mutual coupling between the first and second conductive structures.2. The apparatus of claim 1, wherein the substantial absence of mutualcoupling occurs at least in part when a net sum of the first magneticfield generated by the first conductive structure that intersects thesecond conductive structure is substantially zero.
 3. The apparatus ofclaim 1, wherein the first conductive structure and the secondconductive structure define an area in which the first and secondmagnetic fields at least partially overlap, and wherein the substantialabsence of mutual coupling occurs at least in part when a collectiveeffect of addition and subtraction of the first and second magneticfields is substantially zero.
 4. The apparatus of claim 1, wherein thefirst conductive structure and the second conductive structure areconfigured to wirelessly transmit power at a level sufficient to poweror charge an electric vehicle via the first and second magnetic fields.5. The apparatus of claim 1, wherein the third loop is positioned suchthat substantially a center of the third area is positionedsubstantially over a point between the first loop and the second loop.6. The apparatus of claim 1, wherein the first and second loops comprisefirst and second coils, respectively, the first and second coilsconfigured to be electrically connected to the power source, the powersource configured to apply electric current to the first and secondcoils in the same direction in adjacent portions of the first and secondcoils.
 7. The apparatus of claim 6, wherein the third loop comprises athird coil wound to enclose the third area.
 8. The apparatus of claim 1,wherein the first conductive structure has a substantially horizontallypolarized magnetic moment, and wherein the second conductive structurehas a substantially vertically polarized magnetic moment.
 9. Theapparatus of claim 1, wherein the first and second conductive structuresare capacitively loaded and operable at a resonant frequency, whereinthe resonant frequency is substantially equal to a resonant frequency ofa third conductive structure configured to wirelessly receive power viathe first and second magnetic fields.
 10. The apparatus of claim 1,further comprising: a position detection circuit configured to identifya relative position of a third conductive structure relative to thefirst and second conductive structures; and a controller configured tocontrol the first time-varying electrical current or the secondtime-varying electrical current based on the relative position.
 11. Amethod of wirelessly transmitting power, the method comprising:generating a first magnetic field via a first conductive structure inresponse to receiving a first time-varying electrical current from apower source, the first conductive structure comprising a first loop anda second loop enclosing a first area and a second area, respectively,the first loop having a first surface and the second loop having asecond surface that are substantially coplanar; and generating a secondmagnetic field via a second conductive structure in response toreceiving a second time-varying electrical current from the powersource, the second conductive structure comprising a third loopenclosing a third area, the first and second structures positioned tomaintain a substantial absence of mutual coupling between the first andsecond conductive structures.
 12. The method of claim 11, wherein thesubstantial absence of mutual coupling occurs at least in part when anet sum of the first magnetic field generated by the first conductivestructure that intersects the second conductive structure issubstantially zero.
 13. The method of claim 11, wherein the firstconductive structure and the second conductive structure define an areain which the first and second magnetic fields at least partiallyoverlap, and wherein the substantial absence of mutual coupling occursat least in part when a collective effect of addition and subtraction ofthe first and second magnetic fields is substantially zero.
 14. Themethod of claim 11, wherein generating the first and second magneticfields comprises generating the first and second magnetic fields at alevel sufficient to wirelessly transfer power to power or charge anelectric vehicle.
 15. The method of claim 11, wherein the third loop ispositioned such that substantially a center of the third area ispositioned substantially over a point between the first loop and thesecond loop.
 16. The method of claim 11, wherein the first and secondloops comprise first and second coils, respectively, wherein the methodfurther comprises applying electric current to the first and secondcoils in the same direction in adjacent portions of the first and secondcoils.
 17. The method of claim 16, wherein the third loop comprises athird coil wound to enclose the third area.
 18. The method of claim 11,wherein the first conductive structure has a substantially horizontallypolarized magnetic moment, and wherein the second conductive structurehas a substantially vertically polarized magnetic moment.
 19. The methodof claim 11, wherein the first and second conductive structures arecapacitively loaded and operable at a resonant frequency, wherein theresonant frequency is substantially equal to a resonant frequency of athird conductive structure configured to wirelessly receive power viathe first and second magnetic fields.
 20. The method of claim 11,further comprising: identifying a relative position of a thirdconductive structure relative to the first and second conductivestructures; and controlling the first time-varying electrical current orthe second time-varying electrical current based on the relativeposition.
 21. An apparatus for wirelessly transmitting power, theapparatus comprising: a first means for generating a first magneticfield in response to receiving a first time-varying electrical currentfrom a power source, the first generating means comprising a first loopand a second loop enclosing a first area and a second area,respectively, the first loop having a first surface and the second loophaving a second surface that are substantially coplanar; and a secondmeans for generating a second magnetic field in response to receiving asecond time-varying electrical current from the power source, the secondgenerating means comprising a third loop enclosing a third area, thefirst and second generating means positioned to maintain a substantialabsence of mutual coupling between the first and second generatingmeans.
 22. The apparatus of claim 21, wherein the substantial absence ofmutual coupling occurs at least in part when a net sum of the firstmagnetic field generated by the first generating means that intersectsthe second generating means is substantially zero.
 23. The apparatus ofclaim 21, wherein the first generating means and the second generatingmeans define an area in which the first and second magnetic fields atleast partially overlap, and wherein the substantial absence of mutualcoupling occurs at least in part when a collective effect of additionand subtraction of the first and second magnetic fields is substantiallyzero.
 24. The apparatus of claim 21, wherein the first generating meansand the second generating means comprise means for wirelessly providingpower at a level sufficient to power or charge an electric vehicle viathe first and second magnetic fields.
 25. The apparatus of claim 21,wherein the second generating means is positioned such thatsubstantially a center of the third area is positioned substantiallyover a point between the first loop and the second loop.
 26. Theapparatus of claim 25, further comprising means for applying electriccurrent to the first and second generating means in the same directionin adjacent portions of the first and second generating means.
 27. Theapparatus of claim 21, wherein the first generating means has asubstantially horizontally polarized magnetic moment, and wherein thesecond generating means has a substantially vertically polarizedmagnetic moment.
 28. The apparatus of claim 21, wherein the first andsecond generating means are capacitively loaded and operable at aresonant frequency, wherein the resonant frequency is substantiallyequal to a resonant frequency of a conductive structure configured towirelessly receive power via the first and second magnetic fields.